diff --git a/CHANGELOG.md b/CHANGELOG.md
index fa64a960b..acabba369 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -70,6 +70,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Radio - do not emit change event on already checked radio
 - Calendar - add correct dates DOM parts based on active view [[#1278](https://github.com/IgniteUI/igniteui-webcomponents/issues/1278)]
 - Date-picker, Dropdown & Select - showing the component programmatically in response to an outside click event closes the dropdown popover [#1339](https://github.com/IgniteUI/igniteui-webcomponents/issues/1339)
+- Radio - Initially checked radio by attribute throws error when not being last sibling [#1356](https://github.com/IgniteUI/igniteui-webcomponents/issues/1356)
 
 ## [4.11.1] - 2024-07-03
 ### Changed
diff --git a/src/components/common/mixins/form-associated.ts b/src/components/common/mixins/form-associated.ts
index 6273d254b..5d9ac6cc9 100644
--- a/src/components/common/mixins/form-associated.ts
+++ b/src/components/common/mixins/form-associated.ts
@@ -251,10 +251,10 @@ export function FormAssociatedMixin<T extends Constructor<LitElement>>(
       }
     }
 
-    protected handleInvalid = (event: Event) => {
+    protected handleInvalid(event: Event) {
       event.preventDefault();
       this.invalid = true;
-    };
+    }
 
     protected setFormValue(
       value: string | File | FormData | null,
diff --git a/src/components/radio-group/radio-group.spec.ts b/src/components/radio-group/radio-group.spec.ts
index f31e52746..d00228bf9 100644
--- a/src/components/radio-group/radio-group.spec.ts
+++ b/src/components/radio-group/radio-group.spec.ts
@@ -8,6 +8,7 @@ import {
   arrowUp,
 } from '../common/controllers/key-bindings.js';
 import { defineComponents } from '../common/definitions/defineComponents.js';
+import { first, last } from '../common/util.js';
 import { isFocused, simulateKeyboard } from '../common/utils.spec.js';
 import IgcRadioComponent from '../radio/radio.js';
 import IgcRadioGroupComponent from './radio-group.js';
@@ -194,6 +195,138 @@ describe('Radio Group Component', () => {
         });
       });
     });
+
+    describe('Form integration', () => {
+      let form: HTMLFormElement;
+      let formData: FormData;
+
+      function setFormListener() {
+        form.addEventListener('submit', (event: SubmitEvent) => {
+          event.preventDefault();
+          formData = new FormData(form);
+        });
+      }
+
+      describe('Initial checked state', () => {
+        it('initial checked state through group', async () => {
+          form = await fixture(html`
+            <form>
+              <igc-radio-group name="fruit" value="orange">
+                <igc-radio value="apple">Apple</igc-radio>
+                <igc-radio value="banana">Banana</igc-radio>
+                <igc-radio value="orange">Orange</igc-radio>
+              </igc-radio-group>
+            </form>
+          `);
+          radios = Array.from(form.querySelectorAll(IgcRadioComponent.tagName));
+          setFormListener();
+
+          expect(last(radios).checked).to.be.true;
+
+          form.requestSubmit();
+          expect(formData.get('fruit')).to.equal(last(radios).value);
+        });
+
+        it('initial checked state through radio attribute', async () => {
+          form = await fixture(html`
+            <form>
+              <igc-radio-group name="fruit">
+                <igc-radio value="apple" checked>Apple</igc-radio>
+                <igc-radio value="banana">Banana</igc-radio>
+                <igc-radio value="orange">Orange</igc-radio>
+              </igc-radio-group>
+            </form>
+          `);
+          group = form.querySelector(IgcRadioGroupComponent.tagName)!;
+          radios = Array.from(form.querySelectorAll(IgcRadioComponent.tagName));
+          setFormListener();
+
+          expect(first(radios).checked).to.be.true;
+          expect(group.value).to.equal(first(radios).value);
+
+          form.requestSubmit();
+          expect(formData.get('fruit')).to.equal(first(radios).value);
+        });
+
+        it('initial multiple checked state through radio attribute', async () => {
+          form = await fixture(html`
+            <form>
+              <igc-radio-group name="fruit">
+                <igc-radio value="apple" checked>Apple</igc-radio>
+                <igc-radio value="banana" checked>Banana</igc-radio>
+                <igc-radio value="orange" checked>Orange</igc-radio>
+              </igc-radio-group>
+            </form>
+          `);
+          group = form.querySelector(IgcRadioGroupComponent.tagName)!;
+          radios = Array.from(form.querySelectorAll(IgcRadioComponent.tagName));
+          setFormListener();
+
+          // The last checked member of the group takes over as the default checked
+          expect(last(radios).checked).to.be.true;
+          expect(group.value).to.equal(last(radios).value);
+
+          form.requestSubmit();
+          expect(formData.get('fruit')).to.equal(last(radios).value);
+        });
+
+        it('form reset when bound through group value attribute', async () => {
+          form = await fixture(html`
+            <form>
+              <igc-radio-group name="fruit" value="apple">
+                <igc-radio value="apple">Apple</igc-radio>
+                <igc-radio value="banana">Banana</igc-radio>
+                <igc-radio value="orange">Orange</igc-radio>
+              </igc-radio-group>
+            </form>
+          `);
+          group = form.querySelector(IgcRadioGroupComponent.tagName)!;
+          radios = Array.from(form.querySelectorAll(IgcRadioComponent.tagName));
+          setFormListener();
+
+          expect(first(radios).checked).to.be.true;
+
+          form.requestSubmit();
+          expect(formData.get('fruit')).to.equal(first(radios).value);
+
+          last(radios).click();
+          await elementUpdated(last(radios));
+
+          expect(group.value).to.equal(last(radios).value);
+          form.requestSubmit();
+          expect(formData.get('fruit')).to.equal(last(radios).value);
+
+          form.reset();
+          expect(first(radios).checked).to.be.true;
+          expect(group.value).to.equal(first(radios).value);
+        });
+      });
+
+      describe('Validation state', () => {
+        it('required validator visual state', async () => {
+          form = await fixture(html`
+            <form>
+              <igc-radio-group name="fruit">
+                <igc-radio value="apple" required>Apple</igc-radio>
+                <igc-radio value="banana">Banana</igc-radio>
+                <igc-radio value="orange">Orange</igc-radio>
+              </igc-radio-group>
+            </form>
+          `);
+          group = form.querySelector(IgcRadioGroupComponent.tagName)!;
+          radios = Array.from(form.querySelectorAll(IgcRadioComponent.tagName));
+          setFormListener();
+
+          expect(radios.every((radio) => radio.invalid)).to.be.false;
+
+          form.requestSubmit();
+          expect(radios.every((radio) => radio.invalid)).to.be.true;
+
+          form.reset();
+          expect(radios.every((radio) => radio.invalid)).to.be.false;
+        });
+      });
+    });
   });
 
   function createDefaultGroup() {
diff --git a/src/components/radio-group/radio-group.ts b/src/components/radio-group/radio-group.ts
index efe6e3d5b..8472e9cd7 100644
--- a/src/components/radio-group/radio-group.ts
+++ b/src/components/radio-group/radio-group.ts
@@ -92,6 +92,7 @@ export default class IgcRadioGroupComponent extends LitElement {
 
     if (allRadiosUnchecked && this._value) {
       this._setSelectedRadio();
+      this._setDefaultValue();
     }
   }
 
@@ -103,6 +104,12 @@ export default class IgcRadioGroupComponent extends LitElement {
     }
   }
 
+  private _setDefaultValue() {
+    for (const radio of this._radios) {
+      Object.assign(radio, { _defaultValue: radio.checked });
+    }
+  }
+
   private _setSelectedRadio() {
     for (const radio of this._radios) {
       radio.checked = radio.value === this._value;
diff --git a/src/components/radio/radio.ts b/src/components/radio/radio.ts
index aa09399df..889cee4d9 100644
--- a/src/components/radio/radio.ts
+++ b/src/components/radio/radio.ts
@@ -17,7 +17,13 @@ import { registerComponent } from '../common/definitions/register.js';
 import type { Constructor } from '../common/mixins/constructor.js';
 import { EventEmitterMixin } from '../common/mixins/event-emitter.js';
 import { FormAssociatedRequiredMixin } from '../common/mixins/form-associated-required.js';
-import { createCounter, isLTR, partNameMap, wrap } from '../common/util.js';
+import {
+  createCounter,
+  isLTR,
+  last,
+  partNameMap,
+  wrap,
+} from '../common/util.js';
 import { styles } from './themes/radio.base.css.js';
 import { styles as shared } from './themes/shared/radio.common.css.js';
 import { all } from './themes/themes.js';
@@ -134,7 +140,9 @@ export default class IgcRadioComponent extends FormAssociatedRequiredMixin(
   @property({ type: Boolean })
   public set checked(value: boolean) {
     this._checked = Boolean(value);
-    this._checked ? this._updateCheckedState() : this._updateUncheckedState();
+    if (this.hasUpdated) {
+      this._checked ? this._updateCheckedState() : this._updateUncheckedState();
+    }
   }
 
   public get checked(): boolean {
@@ -171,11 +179,16 @@ export default class IgcRadioComponent extends FormAssociatedRequiredMixin(
 
   public override connectedCallback() {
     super.connectedCallback();
-
-    this._checked = this === this._checkedRadios[0];
     this.updateValidity();
   }
 
+  protected override async firstUpdated() {
+    await this.updateComplete;
+    this._checked && this === last(this._checkedRadios)
+      ? this._updateCheckedState()
+      : this.updateValidity();
+  }
+
   /** Simulates a click on the radio control. */
   public override click() {
     this.input.click();