diff --git a/admin/javascript/src/silverstripe-backend.js b/admin/javascript/src/silverstripe-backend.js
index d11093b37..87ba8cd58 100644
--- a/admin/javascript/src/silverstripe-backend.js
+++ b/admin/javascript/src/silverstripe-backend.js
@@ -1,6 +1,7 @@
 import fetch from 'isomorphic-fetch';
 import es6promise from 'es6-promise';
 import qs from 'qs';
+import merge from 'merge';
 
 es6promise.polyfill();
 
@@ -50,6 +51,8 @@ class SilverStripeBackend {
    *   - responseFormat: the content-type of the response data. Decoding will be handled for you.
    *   - payloadSchema: Definition for how the payload data passed into the created method
    *     will be processed. See "Payload Schema"
+   *   - defaultData: Data to merge into the payload
+   *     (which is passed into the returned method when invoked)
    *
    * # Payload Formats
    *
@@ -257,6 +260,7 @@ class SilverStripeBackend {
       payloadFormat: 'application/x-www-form-url-encoded',
       responseFormat: 'application/json',
       payloadSchema: {},
+      defaultData: {},
     }, endpointSpec);
 
     // Substitute shorcut format values with their full mime types
@@ -270,18 +274,20 @@ class SilverStripeBackend {
       }
     );
 
-    return (data) => {
+    return (data = {}) => {
       const headers = {
         Accept: refinedSpec.responseFormat,
         'Content-Type': refinedSpec.payloadFormat,
       };
 
+      const mergedData = merge.recursive({}, refinedSpec.defaultData, data);
+
       // Replace url placeholders, and add query parameters
       // from the payload based on the schema spec.
       const url = applySchemaToUrl(
         refinedSpec.payloadSchema,
         refinedSpec.url,
-        data,
+        mergedData,
         // Always add full payload data to GET requests.
         // GET requests with a HTTP body are technically legal,
         // but throw an error in the WHATWG fetch() implementation.
@@ -292,7 +298,7 @@ class SilverStripeBackend {
         refinedSpec.payloadFormat,
         // Filter raw data through the defined schema,
         // potentially removing keys because they're
-        applySchemaToData(refinedSpec.payloadSchema, data)
+        applySchemaToData(refinedSpec.payloadSchema, mergedData)
       );
 
       const args = refinedSpec.method.toLowerCase() === 'get'
diff --git a/admin/javascript/src/tests/silverstripe-backend-test.js b/admin/javascript/src/tests/silverstripe-backend-test.js
index a5322f919..7073a073c 100644
--- a/admin/javascript/src/tests/silverstripe-backend-test.js
+++ b/admin/javascript/src/tests/silverstripe-backend-test.js
@@ -4,6 +4,7 @@
 jest.unmock('isomorphic-fetch');
 jest.unmock('../silverstripe-backend');
 jest.unmock('qs');
+jest.unmock('merge');
 
 import backend from '../silverstripe-backend';
 
@@ -191,10 +192,10 @@ describe('SilverStripeBackend', () => {
           two: { urlReplacement: ':two' },
         },
       });
-      const promise = endpoint({
+      endpoint({
         one: 1,
         two: 2,
-        three: 3
+        three: 3,
       });
       expect(mock.post.mock.calls[0][0]).toEqual('http://example.com/1/2/?foo=bar');
       expect(mock.post.mock.calls[0][1]).toEqual('two=2&three=3');
@@ -217,10 +218,10 @@ describe('SilverStripeBackend', () => {
           three: { querystring: true },
         },
       });
-      const promise = endpoint({
+      endpoint({
         one: 1,
         two: 2,
-        three: 3
+        three: 3,
       });
       expect(mock.post.mock.calls[0][0]).toEqual('http://example.com/1/2/?foo=bar&three=3');
       expect(mock.post.mock.calls[0][1]).toEqual('{"two":2}');
@@ -242,16 +243,43 @@ describe('SilverStripeBackend', () => {
           three: { querystring: true },
         },
       });
-      const promise = endpoint({
+      endpoint({
         one: 1,
         two: 2,
-        three: 3
+        three: 3,
       });
       expect(mock.get.mock.calls[0][0]).toEqual('http://example.com/1/2/?foo=bar&two=2&three=3');
       expect(mock.get.mock.calls[0][1]).toEqual({
         Accept: 'application/json',
-        'Content-Type': 'application/x-www-form-url-encoded'
+        'Content-Type': 'application/x-www-form-url-encoded',
       });
     });
+
+    it('should merge defaultData into data argument', () => {
+      const mock = getBackendMock({
+        text: () => Promise.resolve('{"status":"ok"}'),
+        headers: new Headers({
+          'Content-Type': 'application/json',
+        }),
+      });
+      const endpoint = mock.createEndpointFetcher({
+        url: 'http://example.com/',
+        method: 'post',
+        payloadFormat: 'json',
+        defaultData: { one: 1, two: 2, four: { fourOne: true } },
+      });
+      endpoint({
+        two: 'updated',
+        three: 3,
+        four: { fourTwo: true },
+      });
+      expect(mock.post.mock.calls[0][0]).toEqual('http://example.com/');
+      expect(mock.post.mock.calls[0][1]).toEqual(JSON.stringify({
+        one: 1,
+        two: 'updated',
+        four: { fourOne: true, fourTwo: true },
+        three: 3,
+      }));
+    });
   });
 });
diff --git a/npm-shrinkwrap.json b/npm-shrinkwrap.json
index 01a5c6b02..8cc00ceff 100644
--- a/npm-shrinkwrap.json
+++ b/npm-shrinkwrap.json
@@ -12759,6 +12759,10 @@
       "version": "1.1.2",
       "resolved": "https://registry.npmjs.org/json-js/-/json-js-1.1.2.tgz"
     },
+    "merge": {
+      "version": "1.2.0",
+      "resolved": "https://registry.npmjs.org/merge/-/merge-1.2.0.tgz"
+    },
     "merge-stream": {
       "version": "1.0.0",
       "resolved": "https://registry.npmjs.org/merge-stream/-/merge-stream-1.0.0.tgz",
diff --git a/package.json b/package.json
index 93beed996..60ff105bd 100644
--- a/package.json
+++ b/package.json
@@ -46,6 +46,7 @@
     "isomorphic-fetch": "https://registry.npmjs.org/isomorphic-fetch/-/isomorphic-fetch-2.2.1.tgz",
     "jquery-sizes": "^0.33.0",
     "json-js": "^1.1.2",
+    "merge": "^1.2.0",
     "page.js": "^4.13.3",
     "qs": "^6.1.0",
     "react": "^0.14.8",