diff --git a/app/service/rest.py b/app/service/rest.py
index e3f6ac578..0b7ea5591 100644
--- a/app/service/rest.py
+++ b/app/service/rest.py
@@ -56,7 +56,8 @@ from app.dao.service_email_reply_to_dao import (
 from app.dao.service_letter_contact_dao import (
     dao_get_letter_contacts_by_service_id,
     create_or_update_letter_contact,
-    dao_get_letter_contact_by_id
+    dao_get_letter_contact_by_id,
+    add_letter_contact_for_service,
 )
 from app.dao.provider_statistics_dao import get_fragment_count
 from app.dao.users_dao import get_user_by_id
@@ -68,7 +69,10 @@ from app.models import Service, ServiceInboundApi
 from app.schema_validation import validate
 from app.service import statistics
 from app.service.service_inbound_api_schema import service_inbound_api, update_service_inbound_api_schema
-from app.service.service_senders_schema import add_service_email_reply_to_request
+from app.service.service_senders_schema import (
+    add_service_email_reply_to_request,
+    add_service_letter_contact_block_request,
+)
 from app.service.utils import get_whitelist_objects
 from app.service.sender import send_notification_to_service_users
 from app.service.send_notification import send_one_off_notification
@@ -587,6 +591,17 @@ def get_letter_contact_by_id(service_id, letter_contact_id):
     return jsonify(result.serialize()), 200
 
 
+@service_blueprint.route('/<uuid:service_id>/letter-contact', methods=['POST'])
+def add_service_letter_contact(service_id):
+    # validate the service exists, throws ResultNotFound exception.
+    dao_fetch_service_by_id(service_id)
+    form = validate(request.get_json(), add_service_letter_contact_block_request)
+    new_letter_contact = add_letter_contact_for_service(service_id=service_id,
+                                                        contact_block=form['contact_block'],
+                                                        is_default=form.get('is_default', True))
+    return jsonify(data=new_letter_contact.serialize()), 201
+
+
 @service_blueprint.route('/unique', methods=["GET"])
 def is_service_name_unique():
     name, email_from = check_request_args(request)
diff --git a/app/service/service_senders_schema.py b/app/service/service_senders_schema.py
index 57b689099..e0a07b0a4 100644
--- a/app/service/service_senders_schema.py
+++ b/app/service/service_senders_schema.py
@@ -9,3 +9,16 @@ add_service_email_reply_to_request = {
     },
     "required": ["email_address", "is_default"]
 }
+
+
+add_service_letter_contact_block_request = {
+    "$schema": "http://json-schema.org/draft-04/schema#",
+    "description": "POST service letter contact block",
+    "type": "object",
+    "title": "Add new letter contact block for service",
+    "properties": {
+        "contact_block": {"type": "string"},
+        "is_default": {"type": "boolean"}
+    },
+    "required": ["contact_block", "is_default"]
+}
diff --git a/tests/app/service/test_rest.py b/tests/app/service/test_rest.py
index 63149e107..b972d68c7 100644
--- a/tests/app/service/test_rest.py
+++ b/tests/app/service/test_rest.py
@@ -2397,3 +2397,57 @@ def test_get_letter_contact_return_404_when_invalid_contact_id(client, notify_db
                           headers=[('Content-Type', 'application/json'), create_authorization_header()])
 
     assert response.status_code == 404
+
+
+def test_add_service_contact_block(client, sample_service):
+    data = json.dumps({"contact_block": "London, E1 8QS", "is_default": True})
+    response = client.post('/service/{}/letter-contact'.format(sample_service.id),
+                           data=data,
+                           headers=[('Content-Type', 'application/json'), create_authorization_header()])
+
+    assert response.status_code == 201
+    json_resp = json.loads(response.get_data(as_text=True))
+    results = ServiceLetterContact.query.all()
+    assert len(results) == 1
+    assert json_resp['data'] == results[0].serialize()
+
+
+def test_add_service_letter_contact_can_add_multiple_addresses(client, sample_service):
+    first = json.dumps({"contact_block": "London, E1 8QS", "is_default": True})
+    client.post('/service/{}/letter-contact'.format(sample_service.id),
+                data=first,
+                headers=[('Content-Type', 'application/json'), create_authorization_header()])
+
+    second = json.dumps({"contact_block": "Aberdeen, AB23 1XH", "is_default": True})
+    response = client.post('/service/{}/letter-contact'.format(sample_service.id),
+                           data=second,
+                           headers=[('Content-Type', 'application/json'), create_authorization_header()])
+    assert response.status_code == 201
+    json_resp = json.loads(response.get_data(as_text=True))
+    results = ServiceLetterContact.query.all()
+    assert len(results) == 2
+    default = [x for x in results if x.is_default]
+    assert json_resp['data'] == default[0].serialize()
+    first_letter_contact_not_default = [x for x in results if not x.is_default]
+    assert first_letter_contact_not_default[0].contact_block == 'London, E1 8QS'
+
+
+def test_add_service_letter_contact_block_raise_exception_if_no_default(client, sample_service):
+    data = json.dumps({"contact_block": "London, E1 8QS", "is_default": False})
+    response = client.post('/service/{}/letter-contact'.format(sample_service.id),
+                           data=data,
+                           headers=[('Content-Type', 'application/json'), create_authorization_header()])
+    assert response.status_code == 400
+    json_resp = json.loads(response.get_data(as_text=True))
+    assert json_resp['message'] == 'You must have at least one letter contact as the default.'
+
+
+def test_add_service_letter_contact_block_404s_when_invalid_service_id(client, notify_db, notify_db_session):
+    response = client.post('/service/{}/letter-contact'.format(uuid.uuid4()),
+                           data={},
+                           headers=[('Content-Type', 'application/json'), create_authorization_header()])
+
+    assert response.status_code == 404
+    result = json.loads(response.get_data(as_text=True))
+    assert result['result'] == 'error'
+    assert result['message'] == 'No result found'