diff --git a/test/api/v3/integration/groups/POST-groups_groupId_reject.test.js b/test/api/v3/integration/groups/POST-groups_groupId_reject.test.js
new file mode 100644
index 0000000000..27018c24fe
--- /dev/null
+++ b/test/api/v3/integration/groups/POST-groups_groupId_reject.test.js
@@ -0,0 +1,124 @@
+import {
+  generateUser,
+  createAndPopulateGroup,
+  translate as t,
+} from '../../../../helpers/api-v3-integration.helper';
+import { v4 as generateUUID } from 'uuid';
+
+describe('POST /group/:groupId/reject-invite', () => {
+  it('returns error when groupId is not for a valid group', async () => {
+    let userToRejectInvite = await generateUser();
+
+    await expect(userToRejectInvite.post(`/groups/${generateUUID()}/reject-invite`)).to.eventually.be.rejected.and.eql({
+      code: 404,
+      error: 'NotFound',
+      message: t('groupNotFound'),
+    });
+  });
+
+  context('Rejecting a public guild invite', () => {
+    let publicGuild, invitedUser;
+
+    beforeEach(async () => {
+      let {group, invitees} = await createAndPopulateGroup({
+        groupDetails: {
+          name: 'Test Guild',
+          type: 'guild',
+          privacy: 'public',
+        },
+        invites: 1,
+      });
+
+      publicGuild = group;
+      invitedUser = invitees[0];
+    });
+
+    it('returns error when user is not invited', async () => {
+      let userWithoutInvite = await generateUser();
+
+      await expect(userWithoutInvite.post(`/groups/${publicGuild._id}/reject-invite`)).to.eventually.be.rejected.and.eql({
+        code: 401,
+        error: 'NotAuthorized',
+        message: t('messageGroupRequiresInvite'),
+      });
+    });
+
+    it('clears invitation from user', async () => {
+      await invitedUser.post(`/groups/${publicGuild._id}/reject-invite`);
+
+      await expect(invitedUser.get('/user'))
+        .to.eventually.have.deep.property('invitations.guilds')
+        .to.not.include({id: publicGuild._id});
+    });
+  });
+
+  context('Rejecting a private guild invite', () => {
+    let invitedUser, guild;
+
+    beforeEach(async () => {
+      let { group, invitees } = await createAndPopulateGroup({
+        groupDetails: {
+          name: 'Test Guild',
+          type: 'guild',
+          privacy: 'private',
+        },
+        invites: 1,
+      });
+
+      guild = group;
+      invitedUser = invitees[0];
+    });
+
+    it('returns error when user is not invited', async () => {
+      let userWithoutInvite = await generateUser();
+
+      await expect(userWithoutInvite.post(`/groups/${guild._id}/reject-invite`)).to.eventually.be.rejected.and.eql({
+        code: 401,
+        error: 'NotAuthorized',
+        message: t('messageGroupRequiresInvite'),
+      });
+    });
+
+    it('clears invitation from user', async () => {
+      await invitedUser.post(`/groups/${guild._id}/reject-invite`);
+
+      await expect(invitedUser.get('/user'))
+        .to.eventually.have.deep.property('invitations.guilds')
+        .to.not.include({id: guild._id});
+    });
+  });
+
+  context('Rejecting a party invite', () => {
+    let invitedUser, party;
+
+    beforeEach(async () => {
+      let { group, invitees } = await createAndPopulateGroup({
+        groupDetails: {
+          name: 'Test Party',
+          type: 'party',
+        },
+        members: 2,
+        invites: 1,
+      });
+
+      party = group;
+      invitedUser = invitees[0];
+    });
+
+    it('returns error when user is not invited', async () => {
+      let userWithoutInvite = await generateUser();
+
+      await expect(userWithoutInvite.post(`/groups/${party._id}/reject-invite`)).to.eventually.be.rejected.and.eql({
+        code: 401,
+        error: 'NotAuthorized',
+        message: t('messageGroupRequiresInvite'),
+      });
+    });
+
+    it('clears invitation from user', async () => {
+      await invitedUser.post(`/groups/${party._id}/reject-invite`);
+
+      await expect(invitedUser.get('/user')).to.eventually.not.have.deep.property('invitations.party.id');
+    });
+  });
+});
diff --git a/website/src/controllers/api-v3/groups.js b/website/src/controllers/api-v3/groups.js
index 372e0c61fc..6be847a813 100644
--- a/website/src/controllers/api-v3/groups.js
+++ b/website/src/controllers/api-v3/groups.js
@@ -307,6 +307,53 @@ api.joinGroup = {
   },
 };
 
+/**
+ * @api {post} /groups/:groupId/reject Reject a group invitation
+ * @apiVersion 3.0.0
+ * @apiName RejectGroupInvite
+ * @apiGroup Group
+ *
+ * @apiParam {UUID} groupId The group _id
+ *
+ * @apiSuccess {Object} group The group
+ */
+api.rejectGroupInvite = {
+  method: 'POST',
+  url: '/groups/:groupId/reject-invite',
+  middlewares: [authWithHeaders(), cron],
+  async handler (req, res) {
+    let user = res.locals.user;
+
+    req.checkParams('groupId', res.t('groupIdRequired')).notEmpty().isUUID();
+
+    let validationErrors = req.validationErrors();
+    if (validationErrors) throw validationErrors;
+
+    let group = await Group.getGroup({user, groupId: req.params.groupId, optionalMembership: true}); // Do not fetch chat and work even if the user is not yet a member of the group
+    if (!group) throw new NotFound(res.t('groupNotFound'));
+
+    let isUserInvited = false;
+
+    if (group.type === 'party' && group._id === user.invitations.party.id) {
+      user.invitations.party = {};
+      user.markModified('invitations.party');
+      isUserInvited = true;
+    } else if (group.type === 'guild') {
+      let hasInvitation = removeFromArray(user.invitations.guilds, { id: group._id });
+
+      if (hasInvitation) {
+        isUserInvited = true;
+      }
+    }
+
+    if (!isUserInvited) throw new NotAuthorized(res.t('messageGroupRequiresInvite'));
+
+    await user.save();
+
+    res.respond(200, {});
+  },
+};
+
 /**
  * @api {post} /groups/:groupId/leave Leave a group
  * @apiVersion 3.0.0