diff --git a/.swiftpm/xcode/xcshareddata/xcschemes/BrowserServicesKit.xcscheme b/.swiftpm/xcode/xcshareddata/xcschemes/BrowserServicesKit.xcscheme
index b3e79c64a..6c05e98e7 100644
--- a/.swiftpm/xcode/xcshareddata/xcschemes/BrowserServicesKit.xcscheme
+++ b/.swiftpm/xcode/xcshareddata/xcschemes/BrowserServicesKit.xcscheme
@@ -165,15 +165,15 @@
             </BuildableReference>
          </TestableReference>
          <TestableReference
-             skipped = "NO">
-             <BuildableReference
-                BuildableIdentifier = "primary"
-                BlueprintIdentifier = "PhishingDetectionTests"
-                BuildableName = "PhishingDetectionTests"
-                BlueprintName = "PhishingDetectionTests"
-                ReferencedContainer = "container:">
-             </BuildableReference>
-          </TestableReference>
+            skipped = "NO">
+            <BuildableReference
+               BuildableIdentifier = "primary"
+               BlueprintIdentifier = "PhishingDetectionTests"
+               BuildableName = "PhishingDetectionTests"
+               BlueprintName = "PhishingDetectionTests"
+               ReferencedContainer = "container:">
+            </BuildableReference>
+         </TestableReference>
       </Testables>
    </TestAction>
    <LaunchAction
diff --git a/Sources/BrowserServicesKit/Autofill/AutofillUserScript+SecureVault.swift b/Sources/BrowserServicesKit/Autofill/AutofillUserScript+SecureVault.swift
index 1b6ec4699..71f30a3a7 100644
--- a/Sources/BrowserServicesKit/Autofill/AutofillUserScript+SecureVault.swift
+++ b/Sources/BrowserServicesKit/Autofill/AutofillUserScript+SecureVault.swift
@@ -491,6 +491,7 @@ extension AutofillUserScript {
         case userInitiated
         case autoprompt
         case formSubmission
+        case partialSave
         case passwordGeneration
         case emailProtection
     }
diff --git a/Sources/BrowserServicesKit/PrivacyConfig/Features/PrivacyFeature.swift b/Sources/BrowserServicesKit/PrivacyConfig/Features/PrivacyFeature.swift
index 3c6ccc61b..56cdd44e6 100644
--- a/Sources/BrowserServicesKit/PrivacyConfig/Features/PrivacyFeature.swift
+++ b/Sources/BrowserServicesKit/PrivacyConfig/Features/PrivacyFeature.swift
@@ -90,6 +90,7 @@ public enum AutofillSubfeature: String, PrivacySubfeature {
     case onForExistingUsers
     case unknownUsernameCategorization
     case credentialsImportPromotionForExistingUsers
+    case partialFormSaves
 }
 
 public enum DBPSubfeature: String, Equatable, PrivacySubfeature {
diff --git a/Sources/BrowserServicesKit/SecureVault/PartialFormSaveManager.swift b/Sources/BrowserServicesKit/SecureVault/PartialFormSaveManager.swift
new file mode 100644
index 000000000..abbb91f13
--- /dev/null
+++ b/Sources/BrowserServicesKit/SecureVault/PartialFormSaveManager.swift
@@ -0,0 +1,62 @@
+//
+//  PartialFormSaveManager.swift
+//
+//  Copyright © 2024 DuckDuckGo. All rights reserved.
+//
+//  Licensed under the Apache License, Version 2.0 (the "License");
+//  you may not use this file except in compliance with the License.
+//  You may obtain a copy of the License at
+//
+//  http://www.apache.org/licenses/LICENSE-2.0
+//
+//  Unless required by applicable law or agreed to in writing, software
+//  distributed under the License is distributed on an "AS IS" BASIS,
+//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//  See the License for the specific language governing permissions and
+//  limitations under the License.
+//
+
+import Foundation
+import Common
+
+final class PartialFormSaveManager {
+    typealias WebsiteAccount = SecureVaultModels.WebsiteAccount
+
+    private static var accounts: [String: WebsiteAccount] = .init()
+
+    private let tld: TLD
+
+    init(tld: TLD) {
+        self.tld = tld
+    }
+
+    func partialAccount(forDomain domain: String) -> WebsiteAccount? {
+        guard let tldPlus1 = tld.eTLDplus1(domain) else {
+            return nil
+        }
+        guard let account = Self.accounts[tldPlus1] else {
+            return nil
+        }
+
+        guard account.lastUpdated.isLessThan(minutesAgo: 3) else {
+            Self.accounts.removeValue(forKey: domain)
+            return nil
+        }
+
+        return account
+    }
+
+    func store(partialAccount: WebsiteAccount, for domain: String) {
+        guard let tldPlus1 = tld.eTLDplus1(domain) else {
+            return
+        }
+        Self.accounts[tldPlus1] = partialAccount
+    }
+
+    func removePartialAccount(for domain: String) {
+        guard let tldPlus1 = tld.eTLDplus1(domain) else {
+            return
+        }
+        Self.accounts.removeValue(forKey: tldPlus1)
+    }
+}
diff --git a/Sources/BrowserServicesKit/SecureVault/SecureVaultManager.swift b/Sources/BrowserServicesKit/SecureVault/SecureVaultManager.swift
index 2c4be3389..ed9c69168 100644
--- a/Sources/BrowserServicesKit/SecureVault/SecureVaultManager.swift
+++ b/Sources/BrowserServicesKit/SecureVault/SecureVaultManager.swift
@@ -106,6 +106,8 @@ public class SecureVaultManager {
     // This property can be removed once all platforms will search for partial account matches as the default expected behaviour.
     private let includePartialAccountMatches: Bool
 
+    private let shouldAllowPartialFormSaves: Bool
+
     public let tld: TLD?
 
     // Keeps track of partial account created from autogenerated credentials (Private Email + Pwd)
@@ -121,6 +123,7 @@ public class SecureVaultManager {
     private var autogeneratedCredentials: Bool {
         return autogeneratedUserName || autogeneratedPassword
     }
+    private let partialFormSaveManager: PartialFormSaveManager
 
     public lazy var autofillWebsiteAccountMatcher: AutofillWebsiteAccountMatcher? = {
         guard let tld = tld else { return nil }
@@ -131,11 +134,18 @@ public class SecureVaultManager {
     public init(vault: (any AutofillSecureVault)? = nil,
                 passwordManager: PasswordManager? = nil,
                 includePartialAccountMatches: Bool = false,
+                shouldAllowPartialFormSaves: Bool = false,
                 tld: TLD? = nil) {
         self.vault = vault
         self.passwordManager = passwordManager
         self.includePartialAccountMatches = includePartialAccountMatches
+        self.shouldAllowPartialFormSaves = shouldAllowPartialFormSaves
         self.tld = tld
+        if let tld {
+            partialFormSaveManager = PartialFormSaveManager(tld: tld)
+        } else {
+            partialFormSaveManager = PartialFormSaveManager(tld: TLD())
+        }
     }
 
 }
@@ -213,6 +223,19 @@ extension SecureVaultManager: AutofillSecureVaultDelegate {
             }
 
             var autofilldata = data
+
+            if shouldAllowPartialFormSaves,
+               let partialAccountUsername = partialFormSaveManager.partialAccount(forDomain: domain)?.username,
+               !partialAccountUsername.isEmpty,
+               let credentials = autofilldata.credentials,
+               credentials.username.isNilOrEmpty {
+                autofilldata.credentials = .init(
+                    username: partialAccountUsername,
+                    password: credentials.password,
+                    autogenerated: credentials.autogenerated
+                )
+            }
+
             let vault = try? self.vault ?? AutofillSecureVaultFactory.makeVault(reporter: self.delegate)
             var autoSavedCredentials: SecureVaultModels.WebsiteCredentials?
 
@@ -240,17 +263,13 @@ extension SecureVaultManager: AutofillSecureVaultDelegate {
                 autosaveAccount = nil
             }
 
-            if autofilldata.trigger == .emailProtection {
+            switch autofilldata.trigger {
+            case .emailProtection:
                 autogeneratedUserName = data.credentials?.autogenerated ?? false
-            }
-
-            if autofilldata.trigger == .passwordGeneration {
+            case .passwordGeneration:
                 autogeneratedPassword = data.credentials?.autogenerated ?? false
                 NotificationCenter.default.post(name: .autofillFillEvent, object: nil)
-            }
-
-            // Account for cases when the user has manually changed an autogenerated password or private email
-            if autofilldata.trigger == .formSubmission {
+            case .formSubmission:
                 if autosaveAccount != nil, let credentials = autoSavedCredentials {
 
                     let existingUsername = credentials.account.username
@@ -267,6 +286,13 @@ extension SecureVaultManager: AutofillSecureVaultDelegate {
                     }
 
                 }
+            case .partialSave:
+                guard shouldAllowPartialFormSaves else { return }
+                let username = data.credentials?.username ?? data.identity?.emailAddress
+                let partialAccount = SecureVaultModels.WebsiteAccount(username: username, domain: domain)
+                partialFormSaveManager.store(partialAccount: partialAccount, for: domain)
+                return
+            case .none, .userInitiated, .autoprompt: break
             }
 
             autofilldata.credentials?.autogenerated = autogeneratedCredentials
@@ -287,6 +313,7 @@ extension SecureVaultManager: AutofillSecureVaultDelegate {
                     delegate?.secureVaultManager(self, promptUserToStoreAutofillData: dataToPrompt, withTrigger: data.trigger)
                     autosaveAccount = nil
                     autosaveAccountCreatedInSession = false
+                    partialFormSaveManager.removePartialAccount(for: domain)
                 }
                 return
             } else {
@@ -304,6 +331,7 @@ extension SecureVaultManager: AutofillSecureVaultDelegate {
                     dataToPrompt.automaticallySavedCredentials = autogeneratedCredentials
                     autosaveAccount = nil
                     autosaveAccountCreatedInSession = false
+                    partialFormSaveManager.removePartialAccount(for: domain)
                 }
                 delegate?.secureVaultManager(self, promptUserToStoreAutofillData: dataToPrompt, withTrigger: autofilldata.trigger)
             }
@@ -676,12 +704,11 @@ extension SecureVaultManager: AutofillSecureVaultDelegate {
 
         guard let accounts = try? vault.accountsFor(domain: domain),
               // Matching account (username) or account with empty username for domain
-              var account = accounts.first(where: { $0.username == credentials.username || $0.username == "" }) else {
+              var account = accounts.first(where: { $0.username == credentials.username || $0.username.isNilOrEmpty }) else {
 
                 // No existing credentials found.  This is a new entry
                 let account = SecureVaultModels.WebsiteAccount(username: credentials.username ?? "", domain: domain)
                 return SecureVaultModels.WebsiteCredentials(account: account, password: passwordData)
-
         }
 
         guard let existingAccountId = account.id,
@@ -702,7 +729,7 @@ extension SecureVaultManager: AutofillSecureVaultDelegate {
         }
 
         // Prompt to update the login on submit when previous username was empty (there was a partial password account)
-        if existingCredentials.account.username == "" {
+        if existingCredentials.account.username.isNilOrEmpty {
             account.username = autofillData.credentials?.username ?? ""
             return SecureVaultModels.WebsiteCredentials(account: account, password: passwordData)
         }
diff --git a/Sources/Common/Extensions/DateExtension.swift b/Sources/Common/Extensions/DateExtension.swift
index 2a4ca74ea..4ae7be7f6 100644
--- a/Sources/Common/Extensions/DateExtension.swift
+++ b/Sources/Common/Extensions/DateExtension.swift
@@ -139,4 +139,8 @@ public extension Date {
         self > Date().addingTimeInterval(Double(-days) * 24 * 60 * 60)
     }
 
+    func isLessThan(minutesAgo minutes: Int) -> Bool {
+        self > Date().addingTimeInterval(Double(-minutes) * 60)
+    }
+
 }
diff --git a/Sources/Common/Extensions/StringExtension.swift b/Sources/Common/Extensions/StringExtension.swift
index 9282a43b4..31a2481c5 100644
--- a/Sources/Common/Extensions/StringExtension.swift
+++ b/Sources/Common/Extensions/StringExtension.swift
@@ -495,3 +495,12 @@ public extension StringProtocol {
     }
 
 }
+
+public extension Optional where Wrapped == String {
+    var isNilOrEmpty: Bool {
+        if case .some(let wrapped) = self {
+            return wrapped.isEmpty
+        }
+        return true
+    }
+}
diff --git a/Tests/BrowserServicesKitTests/SecureVault/MockAutofillDatabaseProvider.swift b/Tests/BrowserServicesKitTests/SecureVault/MockAutofillDatabaseProvider.swift
index d116f3f94..21623f840 100644
--- a/Tests/BrowserServicesKitTests/SecureVault/MockAutofillDatabaseProvider.swift
+++ b/Tests/BrowserServicesKitTests/SecureVault/MockAutofillDatabaseProvider.swift
@@ -19,6 +19,7 @@
 import Foundation
 import GRDB
 import SecureStorage
+import Common
 
 @testable import BrowserServicesKit
 
@@ -57,8 +58,11 @@ internal class MockAutofillDatabaseProvider: AutofillDatabaseProvider {
             _credentialsDict[accountID] = credentials
             return accountID
         } else {
+            var credentialsToStore = credentials
             let id = Int64(_credentialsDict.count + 1)
-            _credentialsDict[id] = credentials
+            credentialsToStore.account.id = String(id)
+            _credentialsDict[id] = credentialsToStore
+            _accounts.append(credentialsToStore.account)
             return id
         }
     }
@@ -68,11 +72,15 @@ internal class MockAutofillDatabaseProvider: AutofillDatabaseProvider {
     }
 
     func websiteCredentialsForDomain(_ domain: String) throws -> [BrowserServicesKit.SecureVaultModels.WebsiteCredentials] {
-        return _credentialsForDomainDict[domain] ?? []
+        return _credentialsForDomainDict[domain] ?? _credentialsDict.values.filter {
+            $0.account.domain == domain
+        }
     }
 
     func websiteCredentialsForTopLevelDomain(_ eTLDplus1: String) throws -> [BrowserServicesKit.SecureVaultModels.WebsiteCredentials] {
-        return _credentialsForDomainDict[eTLDplus1] ?? []
+        return _credentialsForDomainDict[eTLDplus1] ?? _credentialsDict.values.filter {
+            TLD().eTLDplus1($0.account.domain) == eTLDplus1
+        }
     }
 
     func websiteAccountsForDomain(_ domain: String) throws -> [SecureVaultModels.WebsiteAccount] {
diff --git a/Tests/BrowserServicesKitTests/SecureVault/SecureVaultManagerTests.swift b/Tests/BrowserServicesKitTests/SecureVault/SecureVaultManagerTests.swift
index 71e65449a..2da97e0aa 100644
--- a/Tests/BrowserServicesKitTests/SecureVault/SecureVaultManagerTests.swift
+++ b/Tests/BrowserServicesKitTests/SecureVault/SecureVaultManagerTests.swift
@@ -66,7 +66,7 @@ class SecureVaultManagerTests: XCTestCase {
 
         self.testVault = DefaultAutofillSecureVault(providers: providers)
         self.secureVaultManagerDelegate = MockSecureVaultManagerDelegate()
-        self.manager = SecureVaultManager(vault: self.testVault)
+        self.manager = SecureVaultManager(vault: self.testVault, shouldAllowPartialFormSaves: true)
         self.manager.delegate = secureVaultManagerDelegate
     }
 
@@ -854,6 +854,94 @@ class SecureVaultManagerTests: XCTestCase {
 
     }
 
+    func testWhenFormSubmittedWithNilUsername_afterPartialSaveWithUsername_storesAndPromptsWithFullCredentials() {
+        let partialCredentials = AutofillUserScript.IncomingCredentials(username: "email@example.com", password: nil, autogenerated: false)
+        let partialData = AutofillUserScript.DetectedAutofillData(identity: nil, credentials: partialCredentials, creditCard: nil, trigger: .partialSave)
+        manager.autofillUserScript(mockAutofillUserScript, didRequestStoreDataForDomain: "fill.dev", data: partialData)
+
+        var incomingCredentials = AutofillUserScript.IncomingCredentials(username: nil, password: "m4nu4lP4sswOrd", autogenerated: false)
+        var incomingData = AutofillUserScript.DetectedAutofillData(identity: nil, credentials: incomingCredentials, creditCard: nil, trigger: .formSubmission)
+        manager.autofillUserScript(mockAutofillUserScript, didRequestStoreDataForDomain: "fill.dev", data: incomingData)
+
+        // Check stored
+        incomingCredentials = AutofillUserScript.IncomingCredentials(username: "email@example.com", password: "m4nu4lP4sswOrd", autogenerated: false)
+        incomingData = AutofillUserScript.DetectedAutofillData(identity: nil, credentials: incomingCredentials, creditCard: nil, trigger: .formSubmission)
+        let entries = try? manager.existingEntries(for: "fill.dev", autofillData: incomingData)
+        XCTAssertEqual(entries?.credentials?.account.username, "email@example.com")
+        XCTAssertEqual(entries?.credentials?.password, Data("m4nu4lP4sswOrd".utf8))
+
+        // Check prompted
+        XCTAssertNotNil(secureVaultManagerDelegate.promptedAutofillData)
+        XCTAssertEqual(secureVaultManagerDelegate.promptedAutofillData?.credentials?.account.username, "email@example.com")
+        XCTAssertEqual(secureVaultManagerDelegate.promptedAutofillData?.credentials?.password, Data("m4nu4lP4sswOrd".utf8))
+    }
+
+    func testWhenFormSubmittedWithNilUsername_afterPartialSaveWithUsername_domainsDifferent_onlyStoresTheFormSubmission() {
+        let partialCredentials = AutofillUserScript.IncomingCredentials(username: "email@example.com", password: nil, autogenerated: false)
+        let partialData = AutofillUserScript.DetectedAutofillData(identity: nil, credentials: partialCredentials, creditCard: nil, trigger: .partialSave)
+        manager.autofillUserScript(mockAutofillUserScript, didRequestStoreDataForDomain: "dill.fev", data: partialData)
+
+        var incomingCredentials = AutofillUserScript.IncomingCredentials(username: nil, password: "m4nu4lP4sswOrd", autogenerated: false)
+        var incomingData = AutofillUserScript.DetectedAutofillData(identity: nil, credentials: incomingCredentials, creditCard: nil, trigger: .formSubmission)
+        manager.autofillUserScript(mockAutofillUserScript, didRequestStoreDataForDomain: "fill.dev", data: incomingData)
+
+        // Check stored
+        incomingCredentials = AutofillUserScript.IncomingCredentials(username: nil, password: "m4nu4lP4sswOrd", autogenerated: false)
+        incomingData = AutofillUserScript.DetectedAutofillData(identity: nil, credentials: incomingCredentials, creditCard: nil, trigger: .formSubmission)
+        let entries = try? manager.existingEntries(for: "fill.dev", autofillData: incomingData)
+        XCTAssertNotEqual(entries?.credentials?.account.username, "email@example.com")
+        XCTAssertEqual(entries?.credentials?.password, Data("m4nu4lP4sswOrd".utf8))
+
+        // Check prompted
+        XCTAssertNotNil(secureVaultManagerDelegate.promptedAutofillData)
+        XCTAssertNotEqual(secureVaultManagerDelegate.promptedAutofillData?.credentials?.account.username, "email@example.com")
+        XCTAssertEqual(secureVaultManagerDelegate.promptedAutofillData?.credentials?.password, Data("m4nu4lP4sswOrd".utf8))
+    }
+
+    func testWhenFormSubmittedWithNilUsername_afterPartialSaveWithUsername_updatesExistingUsernameOnlyStoredData() {
+        // Check initial stored
+        let initialCredentials = SecureVaultModels.WebsiteCredentials(account: .init(username: "email@example.com", domain: "fill.dev"), password: nil)
+        guard let theID = try? testVault.storeWebsiteCredentials(initialCredentials) else {
+            XCTFail("Couldn't store initial credentials")
+            return
+        }
+
+        let partialCredentials = AutofillUserScript.IncomingCredentials(username: "email@example.com", password: nil, autogenerated: false)
+        let partialData = AutofillUserScript.DetectedAutofillData(identity: nil, credentials: partialCredentials, creditCard: nil, trigger: .partialSave)
+        manager.autofillUserScript(mockAutofillUserScript, didRequestStoreDataForDomain: "fill.dev", data: partialData)
+
+        let incomingCredentials = AutofillUserScript.IncomingCredentials(username: nil, password: "m4nu4lP4sswOrd", autogenerated: false)
+        let incomingData = AutofillUserScript.DetectedAutofillData(identity: nil, credentials: incomingCredentials, creditCard: nil, trigger: .formSubmission)
+        manager.autofillUserScript(mockAutofillUserScript, didRequestStoreDataForDomain: "fill.dev", data: incomingData)
+
+        // Check prompted
+        XCTAssertNotNil(secureVaultManagerDelegate.promptedAutofillData)
+        // Prompting with an account with ID will result in an update
+        XCTAssertEqual(secureVaultManagerDelegate.promptedAutofillData?.credentials?.account.id, String(theID))
+    }
+
+    func testWhenFormSubmittedWithNilUsername_afterPartialSaveWithUsername_updatesExistingPasswordOnlyStoredData() {
+        // Check initial stored
+        let initialCredentials = SecureVaultModels.WebsiteCredentials(account: .init(username: nil, domain: "fill.dev"), password: "m4nu4lP4sswOrd".data(using: .utf8))
+        guard let theID = try? testVault.storeWebsiteCredentials(initialCredentials) else {
+            XCTFail("Couldn't store initial credentials")
+            return
+        }
+
+        let partialCredentials = AutofillUserScript.IncomingCredentials(username: "email@example.com", password: nil, autogenerated: false)
+        let partialData = AutofillUserScript.DetectedAutofillData(identity: nil, credentials: partialCredentials, creditCard: nil, trigger: .partialSave)
+        manager.autofillUserScript(mockAutofillUserScript, didRequestStoreDataForDomain: "fill.dev", data: partialData)
+
+        let incomingCredentials = AutofillUserScript.IncomingCredentials(username: nil, password: "m4nu4lP4sswOrd", autogenerated: false)
+        let incomingData = AutofillUserScript.DetectedAutofillData(identity: nil, credentials: incomingCredentials, creditCard: nil, trigger: .formSubmission)
+        manager.autofillUserScript(mockAutofillUserScript, didRequestStoreDataForDomain: "fill.dev", data: incomingData)
+
+        // Check prompted
+        XCTAssertNotNil(secureVaultManagerDelegate.promptedAutofillData)
+        // Prompting with an account with ID will result in an update
+        XCTAssertEqual(secureVaultManagerDelegate.promptedAutofillData?.credentials?.account.id, String(theID))
+    }
+
     // MARK: - Test Utilities
 
     private func identity(id: Int64? = nil, name: (String, String, String), addressStreet: String?) -> SecureVaultModels.Identity {