diff --git a/app/controllers/constituencies_controller.rb b/app/controllers/constituencies_controller.rb
index 0779c9b19..f93644128 100644
--- a/app/controllers/constituencies_controller.rb
+++ b/app/controllers/constituencies_controller.rb
@@ -1,11 +1,23 @@
 class ConstituenciesController < ApplicationController
   before_action :set_cors_headers, only: [:index], if: :json_request?
+  before_action :fetch_parliament, only: [:index]
 
   def index
-    @constituencies = Constituency.current.by_ons_code
+    @constituencies = @parliament.constituencies.by_ons_code
 
     respond_to do |format|
       format.json
     end
   end
+
+  private
+
+  def fetch_parliament
+    case params[:period]
+    when Parliament::PERIOD_FORMAT
+      @parliament = Parliament.archived.find_by!(period: params[:period])
+    else
+      @parliament = Parliament.instance
+    end
+  end
 end
diff --git a/app/controllers/petitions_controller.rb b/app/controllers/petitions_controller.rb
index c2d9b13f9..d673e53c4 100644
--- a/app/controllers/petitions_controller.rb
+++ b/app/controllers/petitions_controller.rb
@@ -102,7 +102,9 @@ def redirect_to_home_page_if_dissolved
   end
 
   def redirect_to_home_page_unless_opened
-    redirect_to home_url unless Parliament.opened?
+    unless json_request?
+      redirect_to home_url unless Parliament.opened?
+    end
   end
 
   def request_format
diff --git a/app/models/parliament.rb b/app/models/parliament.rb
index 64eca0987..6ccdeed30 100644
--- a/app/models/parliament.rb
+++ b/app/models/parliament.rb
@@ -4,6 +4,7 @@ class Parliament < ActiveRecord::Base
   include ActiveSupport::NumberHelper
 
   CUTOFF_DATE = Date.civil(2015, 5, 7)
+  PERIOD_FORMAT = /\A\d{4}-\d{4}\z/
 
   has_many :petitions, inverse_of: :parliament, class_name: "Archived::Petition"
   has_many :parliament_constituencies
diff --git a/config/routes.rb b/config/routes.rb
index b85e928f8..c1b4cd4ee 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -2,11 +2,15 @@
   constraints Site.constraints_for_public do
     controller 'constituencies' do
       get '/constituencies', action: 'index', as: :constituencies
+
+      constraints period: /\d{4}-\d{4}|current/ do
+        get '/parliaments/:period/constituencies', action: 'index', as: nil
+      end
     end
 
     controller 'parliaments' do
       get '/parliaments', action: 'index', as: :parliaments
-      get '/parliaments/:period', action: 'show'
+      get '/parliaments/:period', action: 'show', constraints: { period: /\d{4}-\d{4}/ }
     end
 
     controller 'topics' do
diff --git a/spec/controllers/constituencies_controller_spec.rb b/spec/controllers/constituencies_controller_spec.rb
index fcf923fba..1f1ab6e57 100644
--- a/spec/controllers/constituencies_controller_spec.rb
+++ b/spec/controllers/constituencies_controller_spec.rb
@@ -30,4 +30,36 @@
       expect(response.headers["Access-Control-Allow-Headers"]).to eq("Origin, X-Requested-With, Content-Type, Accept")
     end
   end
+
+  describe "GET /parliaments/:period/constituencies.json" do
+    before do
+      FactoryBot.create(:parliament, :conservatives_2019)
+
+      get :index, format: "json", params: { period: "2019-2024" }
+    end
+
+    it "responds with 200 OK" do
+      expect(response.status).to eq(200)
+    end
+
+    it "assigns the @constituencies instance variable" do
+      expect(assigns[:constituencies]).not_to be_nil
+    end
+
+    it "renders the constituencies/index template" do
+      expect(response).to render_template("constituencies/index")
+    end
+
+    it "sets the Access-Control-Allow-Origin header to '*'" do
+      expect(response.headers["Access-Control-Allow-Origin"]).to eq("*")
+    end
+
+    it "sets the Access-Control-Allow-Methods header to 'GET'" do
+      expect(response.headers["Access-Control-Allow-Methods"]).to eq("GET")
+    end
+
+    it "sets the Access-Control-Allow-Headers header to 'Origin, X-Requested-With, Content-Type, Accept'" do
+      expect(response.headers["Access-Control-Allow-Headers"]).to eq("Origin, X-Requested-With, Content-Type, Accept")
+    end
+  end
 end
diff --git a/spec/controllers/petitions_controller_spec.rb b/spec/controllers/petitions_controller_spec.rb
index 43a3690e3..12977fcae 100644
--- a/spec/controllers/petitions_controller_spec.rb
+++ b/spec/controllers/petitions_controller_spec.rb
@@ -501,6 +501,11 @@
         get :index
         expect(response).to redirect_to("https://petition.parliament.uk/")
       end
+
+      it "doesn't redirect JSON requests" do
+        get :index, as: :json
+        expect(response).to be_successful
+      end
     end
   end
 
diff --git a/spec/factories.rb b/spec/factories.rb
index 3da3ecbdd..d9b477763 100644
--- a/spec/factories.rb
+++ b/spec/factories.rb
@@ -927,6 +927,19 @@
     trait :archived do
       archived_at { 1.month.ago }
     end
+
+    trait :conservatives_2019 do
+      government { "Conservatives" }
+      state_opening_at { "2019-12-19 11:30:00".in_time_zone }
+      opening_at { "2020-03-03 10:55:00".in_time_zone }
+      archived_at { "2024-10-21 09:00:00".in_time_zone }
+
+      dissolution_heading { "Parliament is dissolving" }
+      dissolution_message { "This means all petitions will close in 2 weeks" }
+      dissolved_heading { "Parliament is dissolved" }
+      dissolved_message { "All petitions are now closed" }
+      dissolution_at { "2024-05-26 20:40:00".in_time_zone }
+    end
   end
 
   factory :tag do