diff --git a/app/main/forms.py b/app/main/forms.py
index ba7a665b7..536a9b672 100644
--- a/app/main/forms.py
+++ b/app/main/forms.py
@@ -43,7 +43,7 @@ from app.main.validators import (
     ValidGovEmail,
 )
 from app.notify_client.models import permissions, roles
-from app.utils import guess_name_from_email_address
+from app.utils import AgreementInfo, guess_name_from_email_address
 
 
 def get_time_value_and_label(future_time):
@@ -720,10 +720,18 @@ class ServicePreviewBranding(StripWhitespaceForm):
     branding_style = HiddenField('branding_style')
 
 
+class GovernmentDomainField(StringField):
+    validators = [KnownGovernmentDomain()]
+
+    def post_validate(self, form, validation_stopped):
+        if self.data and not self.errors:
+            self.data = AgreementInfo(self.data).canonical_domain
+
+
 class ServiceUpdateEmailBranding(StripWhitespaceForm):
     name = StringField('Name of brand')
     text = StringField('Text')
-    domain = StringField('Domain', validators=[KnownGovernmentDomain()])
+    domain = GovernmentDomainField('Domain')
     colour = StringField(
         'Colour',
         validators=[
diff --git a/tests/app/main/views/test_email_branding.py b/tests/app/main/views/test_email_branding.py
index 3e41924ee..797f5a8e5 100644
--- a/tests/app/main/views/test_email_branding.py
+++ b/tests/app/main/views/test_email_branding.py
@@ -150,6 +150,49 @@ def test_cant_create_new_email_branding_with_unknown_domain(
     assert page.select_one('.error-message').text.strip() == (
         'Not a known government domain (you might need to update domains.yml)'
     )
+    assert page.select_one('input[name=domain]')['value'] == (
+        'example.gov.uk'
+    )
+
+
+@pytest.mark.parametrize('posted_domain, persisted_domain', [
+    ('voa.gsi.gov.uk', 'voa.gov.uk'),
+    ('voa.gov.uk', 'voa.gov.uk'),
+    ('hmcts.net', 'hmcts.gov.uk'),
+])
+def test_persists_canonical_domain_when_adding_email_branding(
+    client_request,
+    mocker,
+    fake_uuid,
+    mock_create_email_branding,
+    posted_domain,
+    persisted_domain,
+):
+    mocker.patch('app.main.views.email_branding.persist_logo')
+    mocker.patch('app.main.views.email_branding.delete_temp_files_created_by')
+    data = {
+        'logo': None,
+        'colour': '#ff0000',
+        'text': 'new text',
+        'name': 'new name',
+        'domain': posted_domain,
+        'brand_type': 'org',
+    }
+    client_request.login(platform_admin_user(fake_uuid))
+    client_request.post(
+        '.create_email_branding',
+        content_type='multipart/form-data',
+        _data=data,
+    )
+
+    assert mock_create_email_branding.call_args == call(
+        logo=data['logo'],
+        name=data['name'],
+        text=data['text'],
+        colour=data['colour'],
+        domain=persisted_domain,
+        brand_type=data['brand_type']
+    )
 
 
 def test_create_new_email_branding_when_branding_saved(