diff --git a/db/migrate/20250910061324_add_duo_default_namespace_id_to_user_preferences.rb b/db/migrate/20250910061324_add_duo_default_namespace_id_to_user_preferences.rb
new file mode 100644
index 0000000000000000000000000000000000000000..91759bb7c53641234b787a61b31dc5a79f1b1f1a
--- /dev/null
+++ b/db/migrate/20250910061324_add_duo_default_namespace_id_to_user_preferences.rb
@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+class AddDuoDefaultNamespaceIdToUserPreferences < Gitlab::Database::Migration[2.3]
+  milestone '18.5'
+
+  def change
+    add_column :user_preferences, :duo_default_namespace_id, :bigint
+  end
+end
diff --git a/db/post_migrate/20250910061326_index_user_preferences_on_duo_default_namespace_id.rb b/db/post_migrate/20250910061326_index_user_preferences_on_duo_default_namespace_id.rb
new file mode 100644
index 0000000000000000000000000000000000000000..b84176519d09bc8ed49d78f943f77c16c24e2485
--- /dev/null
+++ b/db/post_migrate/20250910061326_index_user_preferences_on_duo_default_namespace_id.rb
@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+class IndexUserPreferencesOnDuoDefaultNamespaceId < Gitlab::Database::Migration[2.3]
+  milestone '18.5'
+  disable_ddl_transaction!
+
+  INDEX_NAME = 'index_user_preferences_on_duo_default_namespace_id'
+
+  def up
+    add_concurrent_index :user_preferences, :duo_default_namespace_id, name: INDEX_NAME
+  end
+
+  def down
+    remove_concurrent_index_by_name :user_preferences, INDEX_NAME
+  end
+end
diff --git a/db/post_migrate/20250910061327_add_user_preferences_duo_default_namespace_id_fk.rb b/db/post_migrate/20250910061327_add_user_preferences_duo_default_namespace_id_fk.rb
new file mode 100644
index 0000000000000000000000000000000000000000..57beffacc7720e10d9f227eb00a3bd464c14b133
--- /dev/null
+++ b/db/post_migrate/20250910061327_add_user_preferences_duo_default_namespace_id_fk.rb
@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+class AddUserPreferencesDuoDefaultNamespaceIdFk < Gitlab::Database::Migration[2.3]
+  milestone '18.5'
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_foreign_key :user_preferences, :namespaces, column: :duo_default_namespace_id, on_delete: :nullify
+  end
+
+  def down
+    remove_foreign_key_if_exists :user_preferences, column: :duo_default_namespace_id
+  end
+end
diff --git a/db/schema_migrations/20250910061324 b/db/schema_migrations/20250910061324
new file mode 100644
index 0000000000000000000000000000000000000000..8c33a8605e764528edfffbc4d37de5181914cf5c
--- /dev/null
+++ b/db/schema_migrations/20250910061324
@@ -0,0 +1 @@
+703a1011eba878596f10ca7a0e9dc1555862201873ede9676a837a89748aad43
\ No newline at end of file
diff --git a/db/schema_migrations/20250910061326 b/db/schema_migrations/20250910061326
new file mode 100644
index 0000000000000000000000000000000000000000..c2edb8376adbcedab521818699a54016ba93d8f6
--- /dev/null
+++ b/db/schema_migrations/20250910061326
@@ -0,0 +1 @@
+51e7991206f4dccf19433e35f42b5a426929797f02b87799033d0801baeb94fc
\ No newline at end of file
diff --git a/db/schema_migrations/20250910061327 b/db/schema_migrations/20250910061327
new file mode 100644
index 0000000000000000000000000000000000000000..2b8f0dd27078b6b7048927277e61294e0f69b500
--- /dev/null
+++ b/db/schema_migrations/20250910061327
@@ -0,0 +1 @@
+cca41f500029c11dcaacb88043ab2201502bf515a499197355e4caa47eac16aa
\ No newline at end of file
diff --git a/db/structure.sql b/db/structure.sql
index b22b7802381f957863e323b3fbb247ba42f108c4..478c7d56b62ee5c46191d959b07e5428710bdc99 100644
--- a/db/structure.sql
+++ b/db/structure.sql
@@ -26626,6 +26626,7 @@ CREATE TABLE user_preferences (
     markdown_maintain_indentation boolean DEFAULT false NOT NULL,
     project_studio_enabled boolean DEFAULT false NOT NULL,
     merge_request_dashboard_show_drafts boolean DEFAULT true NOT NULL,
+    duo_default_namespace_id bigint,
     CONSTRAINT check_1d670edc68 CHECK ((time_display_relative IS NOT NULL)),
     CONSTRAINT check_89bf269f41 CHECK ((char_length(diffs_deletion_color) <= 7)),
     CONSTRAINT check_9b50d9f942 CHECK ((char_length(extensions_marketplace_opt_in_url) <= 512)),
@@ -41268,6 +41269,8 @@ CREATE INDEX index_user_phone_number_validations_on_telesign_reference_xid ON us
 
 CREATE INDEX index_user_phone_validations_on_dial_code_phone_number ON user_phone_number_validations USING btree (international_dial_code, phone_number);
 
+CREATE INDEX index_user_preferences_on_duo_default_namespace_id ON user_preferences USING btree (duo_default_namespace_id);
+
 CREATE INDEX index_user_preferences_on_gitpod_enabled ON user_preferences USING btree (gitpod_enabled);
 
 CREATE INDEX index_user_preferences_on_home_organization_id ON user_preferences USING btree (home_organization_id);
@@ -46655,6 +46658,9 @@ ALTER TABLE ONLY deployment_approvals
 ALTER TABLE ONLY dast_profile_schedules
     ADD CONSTRAINT fk_61d52aa0e7 FOREIGN KEY (dast_profile_id) REFERENCES dast_profiles(id) ON DELETE CASCADE;
 
+ALTER TABLE ONLY user_preferences
+    ADD CONSTRAINT fk_61f4fd80d1 FOREIGN KEY (duo_default_namespace_id) REFERENCES namespaces(id) ON DELETE SET NULL;
+
 ALTER TABLE ONLY vulnerability_reads
     ADD CONSTRAINT fk_62736f638f FOREIGN KEY (vulnerability_id) REFERENCES vulnerabilities(id) ON DELETE CASCADE;