diff --git a/app/services/namespaces/projects/create_service.rb b/app/services/namespaces/projects/create_service.rb
index 015e72508..d82892a94 100644
--- a/app/services/namespaces/projects/create_service.rb
+++ b/app/services/namespaces/projects/create_service.rb
@@ -51,9 +51,30 @@ def execute
             }
           )
 
+          assign_runtime_if_unambiguous(project)
+
           ServiceResponse.success(message: 'Created new project', payload: project)
         end
       end
+
+      private
+
+      def assign_runtime_if_unambiguous(project)
+        runtime = runtime_to_assign
+        return if runtime.nil?
+
+        Namespaces::Projects::AssignRuntimesService.new(current_authentication, project, [runtime]).execute
+      end
+
+      def runtime_to_assign
+        global_runtimes = Runtime.where(namespace: nil)
+        namespace_runtimes = namespace.runtimes
+
+        return nil if global_runtimes.exists? && namespace_runtimes.exists?
+        return global_runtimes.first if global_runtimes.one?
+
+        namespace_runtimes.first if namespace_runtimes.one?
+      end
     end
   end
 end
diff --git a/app/services/runtimes/create_service.rb b/app/services/runtimes/create_service.rb
index 74a75bfc5..f98953cde 100644
--- a/app/services/runtimes/create_service.rb
+++ b/app/services/runtimes/create_service.rb
@@ -33,22 +33,8 @@ def execute
           target: namespace || AuditEvent::GLOBAL_TARGET
         )
 
-        assign_as_primary_if_only_runtime(runtime)
-
         ServiceResponse.success(payload: runtime)
       end
     end
-
-    private
-
-    def assign_as_primary_if_only_runtime(runtime)
-      return if namespace.nil?
-      return unless namespace.runtimes.one?
-
-      namespace.projects.where(primary_runtime_id: nil).find_each do |project|
-        project.runtimes << runtime unless project.runtimes.include?(runtime)
-        project.update!(primary_runtime: runtime)
-      end
-    end
   end
 end
diff --git a/spec/services/namespaces/projects/create_service_spec.rb b/spec/services/namespaces/projects/create_service_spec.rb
index d9ed155a3..d40e85bb0 100644
--- a/spec/services/namespaces/projects/create_service_spec.rb
+++ b/spec/services/namespaces/projects/create_service_spec.rb
@@ -100,5 +100,96 @@
         end
       end
     end
+
+    context 'when only one global runtime exists' do
+      let!(:global_runtime) { create(:runtime, namespace: nil) }
+
+      context 'when user has permission to assign runtimes' do
+        before do
+          stub_allowed_ability(
+            NamespaceProjectPolicy, :assign_project_runtimes,
+            user: current_user, subject: an_instance_of(NamespaceProject)
+          )
+        end
+
+        it 'assigns the global runtime as the primary runtime' do
+          service_response
+          expect(service_response.payload.primary_runtime).to eq(global_runtime)
+        end
+
+        it 'assigns the global runtime to the project' do
+          service_response
+          expect(service_response.payload.runtimes).to contain_exactly(global_runtime)
+        end
+      end
+
+      context 'when user does not have permission to assign runtimes' do
+        it 'does not assign a primary runtime' do
+          service_response
+          expect(service_response.payload.primary_runtime).to be_nil
+        end
+      end
+    end
+
+    context 'when multiple global runtimes exist' do
+      before do
+        create(:runtime, namespace: nil)
+        create(:runtime, namespace: nil)
+      end
+
+      it 'does not assign a primary runtime' do
+        service_response
+        expect(service_response.payload.primary_runtime).to be_nil
+      end
+    end
+
+    context 'when no global runtime exists and namespace has exactly one runtime' do
+      let!(:namespace_runtime) { create(:runtime, namespace: namespace) }
+
+      before do
+        stub_allowed_ability(
+          NamespaceProjectPolicy, :assign_project_runtimes,
+          user: current_user, subject: an_instance_of(NamespaceProject)
+        )
+      end
+
+      it 'assigns the namespace runtime as the primary runtime' do
+        service_response
+        expect(service_response.payload.primary_runtime).to eq(namespace_runtime)
+      end
+
+      it 'assigns the namespace runtime to the project' do
+        service_response
+        expect(service_response.payload.runtimes).to contain_exactly(namespace_runtime)
+      end
+    end
+
+    context 'when no global runtime exists and namespace has multiple runtimes' do
+      before do
+        create(:runtime, namespace: namespace)
+        create(:runtime, namespace: namespace)
+      end
+
+      it 'does not assign a primary runtime' do
+        service_response
+        expect(service_response.payload.primary_runtime).to be_nil
+      end
+    end
+
+    context 'when a global runtime exists and the namespace also has a runtime' do
+      before do
+        create(:runtime, namespace: nil)
+        create(:runtime, namespace: namespace)
+        stub_allowed_ability(
+          NamespaceProjectPolicy, :assign_project_runtimes,
+          user: current_user, subject: an_instance_of(NamespaceProject)
+        )
+      end
+
+      it 'does not assign a primary runtime' do
+        service_response
+        expect(service_response.payload.primary_runtime).to be_nil
+      end
+    end
   end
 end
diff --git a/spec/services/runtimes/create_service_spec.rb b/spec/services/runtimes/create_service_spec.rb
index 10fcdcdb5..220475c60 100644
--- a/spec/services/runtimes/create_service_spec.rb
+++ b/spec/services/runtimes/create_service_spec.rb
@@ -71,65 +71,6 @@
     end
   end
 
-  context 'when namespace has a project without a primary runtime' do
-    let(:namespace) { create(:namespace) }
-    let(:current_user) { create(:user) }
-    let(:params) do
-      { name: generate(:runtime_name) }
-    end
-    let!(:project) { create(:namespace_project, namespace: namespace) }
-
-    before do
-      stub_allowed_ability(NamespacePolicy, :create_runtime, user: current_user, subject: namespace)
-    end
-
-    it 'assigns the created runtime as the primary runtime' do
-      service_response
-      expect(project.reload.primary_runtime).to eq(service_response.payload)
-    end
-
-    it 'assigns the created runtime to the project' do
-      service_response
-      expect(project.reload.runtimes).to contain_exactly(service_response.payload)
-    end
-  end
-
-  context 'when namespace already has a runtime' do
-    let(:namespace) { create(:namespace) }
-    let(:current_user) { create(:user) }
-    let(:params) do
-      { name: generate(:runtime_name) }
-    end
-    let!(:existing_runtime) { create(:runtime, namespace: namespace) }
-    let!(:project) { create(:namespace_project, namespace: namespace, primary_runtime: existing_runtime) }
-
-    before do
-      stub_allowed_ability(NamespacePolicy, :create_runtime, user: current_user, subject: namespace)
-    end
-
-    it 'does not change the primary runtime of existing projects' do
-      expect { service_response }.not_to(change { project.reload.primary_runtime })
-    end
-  end
-
-  context 'when project in namespace already has a primary runtime' do
-    let(:namespace) { create(:namespace) }
-    let(:current_user) { create(:user) }
-    let(:params) do
-      { name: generate(:runtime_name) }
-    end
-    let!(:other_runtime) { create(:runtime) }
-    let!(:project) { create(:namespace_project, namespace: namespace, primary_runtime: other_runtime) }
-
-    before do
-      stub_allowed_ability(NamespacePolicy, :create_runtime, user: current_user, subject: namespace)
-    end
-
-    it 'does not change the primary runtime' do
-      expect { service_response }.not_to(change { project.reload.primary_runtime })
-    end
-  end
-
   context 'when user and params are valid and user is admin' do
     let(:current_user) { create(:user, :admin) }
     let(:params) do