diff --git a/src/SlashCommands.tsx b/src/SlashCommands.tsx
index 6b5f2613744..06468c135e1 100644
--- a/src/SlashCommands.tsx
+++ b/src/SlashCommands.tsx
@@ -20,6 +20,7 @@ limitations under the License.
 
 import * as React from 'react';
 
+import { ContentHelpers } from 'matrix-js-sdk';
 import {MatrixClientPeg} from './MatrixClientPeg';
 import dis from './dispatcher/dispatcher';
 import * as sdk from './index';
@@ -126,10 +127,10 @@ export class Command {
         return this.getCommand() + " " + this.args;
     }
 
-    run(roomId: string, args: string, cmd: string) {
+    run(roomId: string, args: string) {
         // if it has no runFn then its an ignored/nop command (autocomplete only) e.g `/me`
         if (!this.runFn) return reject(_t("Command error"));
-        return this.runFn.bind(this)(roomId, args, cmd);
+        return this.runFn.bind(this)(roomId, args);
     }
 
     getUsage() {
@@ -163,7 +164,7 @@ export const Commands = [
             if (args) {
                 message = message + ' ' + args;
             }
-            return success(MatrixClientPeg.get().sendTextMessage(roomId, message));
+            return success(ContentHelpers.makeTextMessage(message));
         },
         category: CommandCategories.messages,
     }),
@@ -176,7 +177,7 @@ export const Commands = [
             if (args) {
                 message = message + ' ' + args;
             }
-            return success(MatrixClientPeg.get().sendTextMessage(roomId, message));
+            return success(ContentHelpers.makeTextMessage(message));
         },
         category: CommandCategories.messages,
     }),
@@ -189,7 +190,7 @@ export const Commands = [
             if (args) {
                 message = message + ' ' + args;
             }
-            return success(MatrixClientPeg.get().sendTextMessage(roomId, message));
+            return success(ContentHelpers.makeTextMessage(message));
         },
         category: CommandCategories.messages,
     }),
@@ -202,7 +203,7 @@ export const Commands = [
             if (args) {
                 message = message + ' ' + args;
             }
-            return success(MatrixClientPeg.get().sendTextMessage(roomId, message));
+            return success(ContentHelpers.makeTextMessage(message));
         },
         category: CommandCategories.messages,
     }),
@@ -211,7 +212,7 @@ export const Commands = [
         args: '<message>',
         description: _td('Sends a message as plain text, without interpreting it as markdown'),
         runFn: function(roomId, messages) {
-            return success(MatrixClientPeg.get().sendTextMessage(roomId, messages));
+            return success(ContentHelpers.makeTextMessage(messages));
         },
         category: CommandCategories.messages,
     }),
@@ -220,7 +221,7 @@ export const Commands = [
         args: '<message>',
         description: _td('Sends a message as html, without interpreting it as markdown'),
         runFn: function(roomId, messages) {
-            return success(MatrixClientPeg.get().sendHtmlMessage(roomId, messages, messages));
+            return success(ContentHelpers.makeHtmlMessage(messages, messages));
         },
         category: CommandCategories.messages,
     }),
@@ -966,7 +967,7 @@ export const Commands = [
         args: '<message>',
         runFn: function(roomId, args) {
             if (!args) return reject(this.getUserId());
-            return success(MatrixClientPeg.get().sendHtmlMessage(roomId, args, textToHtmlRainbow(args)));
+            return success(ContentHelpers.makeHtmlMessage(args, textToHtmlRainbow(args)));
         },
         category: CommandCategories.messages,
     }),
@@ -976,7 +977,7 @@ export const Commands = [
         args: '<message>',
         runFn: function(roomId, args) {
             if (!args) return reject(this.getUserId());
-            return success(MatrixClientPeg.get().sendHtmlEmote(roomId, args, textToHtmlRainbow(args)));
+            return success(ContentHelpers.makeHtmlEmote(args, textToHtmlRainbow(args)));
         },
         category: CommandCategories.messages,
     }),
@@ -1201,10 +1202,13 @@ export function parseCommandString(input: string) {
  * processing the command, or 'promise' if a request was sent out.
  * Returns null if the input didn't match a command.
  */
-export function getCommand(roomId: string, input: string) {
+export function getCommand(input: string) {
     const {cmd, args} = parseCommandString(input);
 
     if (CommandMap.has(cmd) && CommandMap.get(cmd).isEnabled()) {
-        return () => CommandMap.get(cmd).run(roomId, args, cmd);
+        return {
+            cmd: CommandMap.get(cmd),
+            args,
+        };
     }
 }
diff --git a/src/components/views/rooms/SendMessageComposer.js b/src/components/views/rooms/SendMessageComposer.js
index 62c474e417b..d1482c0df62 100644
--- a/src/components/views/rooms/SendMessageComposer.js
+++ b/src/components/views/rooms/SendMessageComposer.js
@@ -33,7 +33,7 @@ import ReplyThread from "../elements/ReplyThread";
 import {parseEvent} from '../../../editor/deserialize';
 import {findEditableEvent} from '../../../utils/EventUtils';
 import SendHistoryManager from "../../../SendHistoryManager";
-import {getCommand} from '../../../SlashCommands';
+import {CommandCategories, getCommand} from '../../../SlashCommands';
 import * as sdk from '../../../index';
 import Modal from '../../../Modal';
 import {_t, _td} from '../../../languageHandler';
@@ -287,15 +287,22 @@ export default class SendMessageComposer extends React.Component {
             }
             return text + part.text;
         }, "");
-        return [getCommand(this.props.room.roomId, commandText), commandText];
+        const {cmd, args} = getCommand(commandText);
+        return [cmd, args, commandText];
     }
 
-    async _runSlashCommand(fn) {
-        const cmd = fn();
-        let error = cmd.error;
-        if (cmd.promise) {
+    async _runSlashCommand(cmd, args) {
+        const result = cmd.run(this.props.room.roomId, args);
+        let messageContent;
+        let error = result.error;
+        if (result.promise) {
             try {
-                await cmd.promise;
+                if (cmd.category === CommandCategories.messages) {
+                    // The command returns a modified message that we need to pass on
+                    messageContent = await result.promise;
+                } else {
+                    await result.promise;
+                }
             } catch (err) {
                 error = err;
             }
@@ -304,7 +311,7 @@ export default class SendMessageComposer extends React.Component {
             console.error("Command failure: %s", error);
             const ErrorDialog = sdk.getComponent("dialogs.ErrorDialog");
             // assume the error is a server error when the command is async
-            const isServerError = !!cmd.promise;
+            const isServerError = !!result.promise;
             const title = isServerError ? _td("Server error") : _td("Command error");
 
             let errText;
@@ -322,6 +329,7 @@ export default class SendMessageComposer extends React.Component {
             });
         } else {
             console.log("Command success.");
+            if (messageContent) return messageContent;
         }
     }
 
@@ -330,13 +338,22 @@ export default class SendMessageComposer extends React.Component {
             return;
         }
 
+        const replyToEvent = this.props.replyToEvent;
         let shouldSend = true;
+        let content;
 
         if (!containsEmote(this.model) && this._isSlashCommand()) {
-            const [cmd, commandText] = this._getSlashCommand();
+            const [cmd, args, commandText] = this._getSlashCommand();
             if (cmd) {
-                shouldSend = false;
-                this._runSlashCommand(cmd);
+                if (cmd.category === CommandCategories.messages) {
+                    content = await this._runSlashCommand(cmd, args);
+                    if (replyToEvent) {
+                        addReplyToMessageContent(content, replyToEvent, this.props.permalinkCreator);
+                    }
+                } else {
+                    this._runSlashCommand(cmd, args);
+                    shouldSend = false;
+                }
             } else {
                 // ask the user if their unknown command should be sent as a message
                 const QuestionDialog = sdk.getComponent("dialogs.QuestionDialog");
@@ -371,11 +388,12 @@ export default class SendMessageComposer extends React.Component {
             this._sendQuickReaction();
         }
 
-        const replyToEvent = this.props.replyToEvent;
         if (shouldSend) {
             const startTime = CountlyAnalytics.getTimestamp();
             const {roomId} = this.props.room;
-            const content = createMessageContent(this.model, this.props.permalinkCreator, replyToEvent);
+            if (!content) {
+                content = createMessageContent(this.model, this.props.permalinkCreator, replyToEvent);
+            }
             // don't bother sending an empty message
             if (!content.body.trim()) return;