diff --git a/res/css/views/dialogs/_DMInviteDialog.scss b/res/css/views/dialogs/_DMInviteDialog.scss
index f806e85120..5d58f3ae8b 100644
--- a/res/css/views/dialogs/_DMInviteDialog.scss
+++ b/res/css/views/dialogs/_DMInviteDialog.scss
@@ -67,6 +67,17 @@ limitations under the License.
         height: 25px;
         line-height: 25px;
     }
+
+    .mx_DMInviteDialog_buttonAndSpinner {
+        .mx_Spinner {
+            // Width and height are required to trick the layout engine.
+            width: 20px;
+            height: 20px;
+            margin-left: 5px;
+            display: inline-block;
+            vertical-align: middle;
+        }
+    }
 }
 
 .mx_DMInviteDialog_section {
diff --git a/src/RoomInvite.js b/src/RoomInvite.js
index 2fe64c994f..8b7324d4f5 100644
--- a/src/RoomInvite.js
+++ b/src/RoomInvite.js
@@ -36,21 +36,19 @@ import SettingsStore from "./settings/SettingsStore";
  * @param {string[]} addrs Array of strings of addresses to invite. May be matrix IDs or 3pids.
  * @returns {Promise} Promise
  */
-function inviteMultipleToRoom(roomId, addrs) {
+export function inviteMultipleToRoom(roomId, addrs) {
     const inviter = new MultiInviter(roomId);
     return inviter.invite(addrs).then(states => Promise.resolve({states, inviter}));
 }
 
 export function showStartChatInviteDialog() {
     if (SettingsStore.isFeatureEnabled("feature_ftue_dms")) {
+        // This new dialog handles the room creation internally - we don't need to worry about it.
         const DMInviteDialog = sdk.getComponent("dialogs.DMInviteDialog");
-        Modal.createTrackedDialog('Start DM', '', DMInviteDialog, {
-            onFinished: (inviteIds) => {
-                // TODO: Replace _onStartDmFinished with less hacks
-                if (inviteIds.length > 0) _onStartDmFinished(true, inviteIds.map(i => ({address: i})));
-                // else ignore and just do nothing
-            },
-        }, /*className=*/null, /*isPriority=*/false, /*isStatic=*/true);
+        Modal.createTrackedDialog(
+            'Start DM', '', DMInviteDialog, {},
+            /*className=*/null, /*isPriority=*/false, /*isStatic=*/true,
+        );
         return;
     }
 
diff --git a/src/components/views/dialogs/DMInviteDialog.js b/src/components/views/dialogs/DMInviteDialog.js
index c0ff9b96fe..2a5c896a75 100644
--- a/src/components/views/dialogs/DMInviteDialog.js
+++ b/src/components/views/dialogs/DMInviteDialog.js
@@ -31,6 +31,8 @@ import dis from "../../../dispatcher";
 import IdentityAuthClient from "../../../IdentityAuthClient";
 import Modal from "../../../Modal";
 import {humanizeTime} from "../../../utils/humanize";
+import createRoom from "../../../createRoom";
+import {inviteMultipleToRoom} from "../../../RoomInvite";
 
 // TODO: [TravisR] Make this generic for all kinds of invites
 
@@ -293,6 +295,10 @@ export default class DMInviteDialog extends React.PureComponent {
             threepidResultsMixin: [], // { user: ThreepidMember, userId: string}[], like recents and suggestions
             canUseIdentityServer: !!MatrixClientPeg.get().getIdentityServerUrl(),
             tryingIdentityServer: false,
+
+            // These two flags are used for the 'Go' button to communicate what is going on.
+            busy: false,
+            errorText: null,
         };
 
         this._editorRef = createRef();
@@ -385,11 +391,64 @@ export default class DMInviteDialog extends React.PureComponent {
     }
 
     _startDm = () => {
-        this.props.onFinished(this.state.targets.map(t => t.userId));
+        this.setState({busy: true});
+        const targetIds = this.state.targets.map(t => t.userId);
+
+        // Check if there is already a DM with these people and reuse it if possible.
+        const existingRoom = DMRoomMap.shared().getDMRoomForIdentifiers(targetIds);
+        if (existingRoom) {
+            dis.dispatch({
+                action: 'view_room',
+                room_id: existingRoom.roomId,
+                should_peek: false,
+                joining: false,
+            });
+            this.props.onFinished();
+            return;
+        }
+
+        // Check if it's a traditional DM and create the room if required.
+        // TODO: [Canonical DMs] Remove this check and instead just create the multi-person DM
+        let createRoomPromise = Promise.resolve();
+        if (targetIds.length === 1) {
+            createRoomPromise = createRoom({dmUserId: targetIds[0]});
+        } else {
+            // Create a boring room and try to invite the targets manually.
+            createRoomPromise = createRoom().then(roomId => {
+                return inviteMultipleToRoom(roomId, targetIds);
+            }).then(result => {
+                const failedUsers = Object.keys(result.states).filter(a => result.states[a] === 'error');
+                if (failedUsers.length > 0) {
+                    console.log("Failed to invite users: ", result);
+                    this.setState({
+                        busy: false,
+                        errorText: _t("Failed to invite the following users to chat: %(csvUsers)s", {
+                            csvUsers: failedUsers.join(", "),
+                        }),
+                    });
+                    return true; // abort
+                }
+            });
+        }
+
+        // the createRoom call will show the room for us, so we don't need to worry about that.
+        createRoomPromise.then(abort => {
+            if (abort === true) return; // only abort on true booleans, not roomIds or something
+            this.props.onFinished();
+        }).catch(err => {
+            console.error(err);
+            this.setState({
+                busy: false,
+                errorText: _t("We couldn't create your DM. Please check the users you want to invite and try again."),
+            });
+        });
     };
 
     _cancel = () => {
-        this.props.onFinished([]);
+        // We do not want the user to close the dialog while an action is in progress
+        if (this.state.busy) return;
+
+        this.props.onFinished();
     };
 
     _updateFilter = (e) => {
@@ -739,6 +798,12 @@ export default class DMInviteDialog extends React.PureComponent {
     render() {
         const BaseDialog = sdk.getComponent('views.dialogs.BaseDialog');
         const AccessibleButton = sdk.getComponent("elements.AccessibleButton");
+        const Spinner = sdk.getComponent("elements.Spinner");
+
+        let spinner = null;
+        if (this.state.busy) {
+            spinner = <Spinner w={20} h={20} />;
+        }
 
         const userId = MatrixClientPeg.get().getUserId();
         return (
@@ -759,15 +824,20 @@ export default class DMInviteDialog extends React.PureComponent {
                     </p>
                     <div className='mx_DMInviteDialog_addressBar'>
                         {this._renderEditor()}
-                        {this._renderIdentityServerWarning()}
-                        <AccessibleButton
-                            kind="primary"
-                            onClick={this._startDm}
-                            className='mx_DMInviteDialog_goButton'
-                        >
-                            {_t("Go")}
-                        </AccessibleButton>
+                        <div className='mx_DMInviteDialog_buttonAndSpinner'>
+                            <AccessibleButton
+                                kind="primary"
+                                onClick={this._startDm}
+                                className='mx_DMInviteDialog_goButton'
+                                disabled={this.state.busy}
+                            >
+                                {_t("Go")}
+                            </AccessibleButton>
+                            {spinner}
+                        </div>
                     </div>
+                    {this._renderIdentityServerWarning()}
+                    <div className='error'>{this.state.errorText}</div>
                     {this._renderSection('recents')}
                     {this._renderSection('suggestions')}
                 </div>
diff --git a/src/i18n/strings/en_EN.json b/src/i18n/strings/en_EN.json
index 3756b4c60b..b6f61570cd 100644
--- a/src/i18n/strings/en_EN.json
+++ b/src/i18n/strings/en_EN.json
@@ -1438,6 +1438,8 @@
     "View Servers in Room": "View Servers in Room",
     "Toolbox": "Toolbox",
     "Developer Tools": "Developer Tools",
+    "Failed to invite the following users to chat: %(csvUsers)s": "Failed to invite the following users to chat: %(csvUsers)s",
+    "We couldn't create your DM. Please check the users you want to invite and try again.": "We couldn't create your DM. Please check the users you want to invite and try again.",
     "Failed to find the following users": "Failed to find the following users",
     "The following users might not exist or are invalid, and cannot be invited: %(csvNames)s": "The following users might not exist or are invalid, and cannot be invited: %(csvNames)s",
     "Recent Conversations": "Recent Conversations",
diff --git a/src/utils/DMRoomMap.js b/src/utils/DMRoomMap.js
index 547da0863b..43ef0035fc 100644
--- a/src/utils/DMRoomMap.js
+++ b/src/utils/DMRoomMap.js
@@ -124,6 +124,27 @@ export default class DMRoomMap {
         return this._getUserToRooms()[userId] || [];
     }
 
+    /**
+     * Gets the DM room which the given IDs share, if any.
+     * @param {string[]} ids The identifiers (user IDs and email addresses) to look for.
+     * @returns {Room} The DM room which all IDs given share, or falsey if no common room.
+     */
+    getDMRoomForIdentifiers(ids) {
+        // TODO: [Canonical DMs] Handle lookups for email addresses.
+        // For now we'll pretend we only get user IDs and end up returning nothing for email addresses
+
+        let commonRooms = this.getDMRoomsForUserId(ids[0]);
+        for (let i = 1; i < ids.length; i++) {
+            const userRooms = this.getDMRoomsForUserId(ids[i]);
+            commonRooms = commonRooms.filter(r => userRooms.includes(r));
+        }
+
+        const joinedRooms = commonRooms.map(r => MatrixClientPeg.get().getRoom(r))
+            .filter(r => r && r.getMyMembership() === 'join');
+
+        return joinedRooms[0];
+    }
+
     getUserIdForRoomId(roomId) {
         if (this.roomToUser == null) {
             // we lazily populate roomToUser so you can use