diff --git a/lib/formslib.php b/lib/formslib.php
index 5b79091d69acf..483db6ea107be 100644
--- a/lib/formslib.php
+++ b/lib/formslib.php
@@ -131,6 +131,9 @@ abstract class moodleform {
     /** @var array globals workaround */
     protected $_customdata;
 
+    /** @var array submitted form data when using mforms with ajax */
+    protected $_ajaxformdata;
+
     /** @var object definition_after_data executed flag */
     protected $_definition_finalized = false;
 
@@ -156,8 +159,9 @@ abstract class moodleform {
      *               it if you don't need to as the target attribute is deprecated in xhtml strict.
      * @param mixed $attributes you can pass a string of html attributes here or an array.
      * @param bool $editable
+     * @param array $ajaxformdata Forms submitted via ajax, must pass their data here, instead of relying on _GET and _POST.
      */
-    public function __construct($action=null, $customdata=null, $method='post', $target='', $attributes=null, $editable=true) {
+    public function __construct($action=null, $customdata=null, $method='post', $target='', $attributes=null, $editable=true, $ajaxformdata=null) {
         global $CFG, $FULLME;
         // no standard mform in moodle should allow autocomplete with the exception of user signup
         if (empty($attributes)) {
@@ -170,6 +174,7 @@ public function __construct($action=null, $customdata=null, $method='post', $tar
             }
         }
 
+
         if (empty($action)){
             // do not rely on PAGE->url here because dev often do not setup $actualurl properly in admin_externalpage_setup()
             $action = strip_querystring($FULLME);
@@ -183,6 +188,7 @@ public function __construct($action=null, $customdata=null, $method='post', $tar
         // Assign custom data first, so that get_form_identifier can use it.
         $this->_customdata = $customdata;
         $this->_formname = $this->get_form_identifier();
+        $this->_ajaxformdata = $ajaxformdata;
 
         $this->_form = new MoodleQuickForm($this->_formname, $method, $action, $target, $attributes);
         if (!$editable){
@@ -272,7 +278,9 @@ function focus($name=NULL) {
      */
     function _process_submission($method) {
         $submission = array();
-        if ($method == 'post') {
+        if (!empty($this->_ajaxformdata) && defined('AJAX_SCRIPT')) {
+            $submission = $this->_ajaxformdata;
+        } else if ($method == 'post') {
             if (!empty($_POST)) {
                 $submission = $_POST;
             }
diff --git a/mod/assign/externallib.php b/mod/assign/externallib.php
index 2f769e144f86b..74a7e94a4b925 100644
--- a/mod/assign/externallib.php
+++ b/mod/assign/externallib.php
@@ -1506,6 +1506,87 @@ public static function unlock_submissions_returns() {
         return new external_warnings();
     }
 
+    /**
+     * Describes the parameters for submit_grading_form webservice.
+     * @return external_external_function_parameters
+     * @since  Moodle 3.1
+     */
+    public static function submit_grading_form_parameters() {
+        return new external_function_parameters(
+            array(
+                'assignmentid' => new external_value(PARAM_INT, 'The assignment id to operate on'),
+                'userid' => new external_value(PARAM_INT, 'The user id the submission belongs to'),
+                'jsonformdata' => new external_value(PARAM_RAW, 'The data from the grading form, encoded as a json array')
+            )
+        );
+    }
+
+    /**
+     * Submit the logged in users assignment for grading.
+     *
+     * @param int $assignmentid The id of the assignment
+     * @param int $userid The id of the user the submission belongs to.
+     * @param string $jsonformdata The data from the form, encoded as a json array.
+     * @return array of warnings to indicate any errors.
+     * @since Moodle 2.6
+     */
+    public static function submit_grading_form($assignmentid, $userid, $jsonformdata) {
+        global $CFG, $USER;
+
+        require_once($CFG->dirroot . '/mod/assign/locallib.php');
+        require_once($CFG->dirroot . '/mod/assign/gradeform.php');
+
+        $params = self::validate_parameters(self::submit_grading_form_parameters(),
+                                            array('assignmentid' => $assignmentid,
+                                                  'userid' => $userid,
+                                                  'jsonformdata' => $jsonformdata));
+
+        $cm = get_coursemodule_from_instance('assign', $params['assignmentid'], 0, false, MUST_EXIST);
+        $context = context_module::instance($cm->id);
+        self::validate_context($context);
+
+        $assignment = new assign($context, $cm, null);
+
+        $serialiseddata = json_decode($params['jsonformdata']);
+
+        $data = array();
+        parse_str($serialiseddata, $data);
+
+        $warnings = array();
+
+        $options = array('userid'=>$params['userid'],
+                         'attemptnumber'=>$data['attemptnumber'],
+                         'rownum'=>0,
+                         'gradingpanel' => true);
+
+        $customdata = (object) $data;
+        $formparams = array($assignment, $customdata, $options);
+
+        // Data is injected into the form by the last param for the constructor.
+        $mform = new mod_assign_grade_form(null, $formparams, 'post', '', null, true, $data);
+        $validateddata = $mform->get_data();
+
+        if ($validateddata) {
+            $assignment->save_grade($params['userid'], $validateddata);
+        } else {
+            $warnings[] = self::generate_warning($params['assignmentid'],
+                                                 'couldnotsavegrade',
+                                                 'Form validation failed.');
+        }
+
+
+        return $warnings;
+    }
+
+    /**
+     * Describes the return for submit_grading_form
+     * @return external_external_function_parameters
+     * @since  Moodle 3.1
+     */
+    public static function submit_grading_form_returns() {
+        return new external_warnings();
+    }
+
     /**
      * Describes the parameters for submit_for_grading
      * @return external_external_function_parameters