diff --git a/app/components/autocomplete/at_mention/at_mention.js b/app/components/autocomplete/at_mention/at_mention.js
index a84470f8f..7e045f59f 100644
--- a/app/components/autocomplete/at_mention/at_mention.js
+++ b/app/components/autocomplete/at_mention/at_mention.js
@@ -222,6 +222,7 @@ export default class AtMention extends PureComponent {
     renderItem = ({item}) => {
         return (
             <AtMentionItem
+                testID={`autocomplete.at_mention.item.${item}`}
                 onPress={this.completeMention}
                 userId={item}
             />
diff --git a/app/components/autocomplete/at_mention_item/at_mention_item.js b/app/components/autocomplete/at_mention_item/at_mention_item.js
index b745e5331..dfe3099b2 100644
--- a/app/components/autocomplete/at_mention_item/at_mention_item.js
+++ b/app/components/autocomplete/at_mention_item/at_mention_item.js
@@ -29,6 +29,7 @@ export default class AtMentionItem extends PureComponent {
         isLandscape: PropTypes.bool.isRequired,
         isCurrentUser: PropTypes.bool.isRequired,
         showFullName: PropTypes.string,
+        testID: PropTypes.string,
     };
 
     static defaultProps = {
@@ -66,6 +67,7 @@ export default class AtMentionItem extends PureComponent {
             isLandscape,
             isGuest,
             isCurrentUser,
+            testID,
         } = this.props;
 
         const style = getStyleFromTheme(theme);
@@ -73,6 +75,7 @@ export default class AtMentionItem extends PureComponent {
 
         return (
             <TouchableWithFeedback
+                testID={testID}
                 key={userId}
                 onPress={this.completeMention}
                 style={padding(isLandscape)}
diff --git a/app/constants/autocomplete.js b/app/constants/autocomplete.js
index 57d0a3fd7..269b7c3db 100644
--- a/app/constants/autocomplete.js
+++ b/app/constants/autocomplete.js
@@ -1,9 +1,9 @@
 // Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
 // See LICENSE.txt for license information.
 
-export const AT_MENTION_REGEX = /\B(@([^@\r\n\s]*))$/i;
+export const AT_MENTION_REGEX = /\B(@([^@\r\n]*))$/i;
 
-export const AT_MENTION_REGEX_GLOBAL = /\B(@([^@\r\n\s]*))/gi;
+export const AT_MENTION_REGEX_GLOBAL = /\B(@([^@\r\n]*))/gi;
 
 export const AT_MENTION_SEARCH_REGEX = /\bfrom:\s*(\S*)$/i;
 
diff --git a/app/selectors/autocomplete.js b/app/selectors/autocomplete.js
index c9d07e2be..5e9c896a1 100644
--- a/app/selectors/autocomplete.js
+++ b/app/selectors/autocomplete.js
@@ -73,9 +73,11 @@ export const filterMembersInChannel = createSelector(
         let profiles;
         if (matchTerm) {
             profiles = profilesInChannel.filter((p) => {
+                const fullName = `${p.first_name.toLowerCase()} ${p.last_name.toLowerCase()}`;
                 return (p.delete_at === 0 && (
                     p.username.toLowerCase().includes(matchTerm) || p.email.toLowerCase().includes(matchTerm) ||
                     p.first_name.toLowerCase().includes(matchTerm) || p.last_name.toLowerCase().includes(matchTerm) ||
+                    fullName.includes(matchTerm) ||
                     p.nickname.toLowerCase().includes(matchTerm)));
             });
         } else {
@@ -98,10 +100,12 @@ export const filterMembersNotInChannel = createSelector(
         let profiles;
         if (matchTerm) {
             profiles = profilesNotInChannel.filter((p) => {
+                const fullName = `${p.first_name.toLowerCase()} ${p.last_name.toLowerCase()}`;
                 return (
                     p.username.toLowerCase().includes(matchTerm) ||
                     p.email.toLowerCase().includes(matchTerm) ||
                     p.first_name.toLowerCase().includes(matchTerm) ||
+                    fullName.includes(matchTerm) ||
                     p.last_name.toLowerCase().includes(matchTerm) ||
                     p.nickname.toLowerCase().includes(matchTerm)
                 ) && p.delete_at === 0;
diff --git a/app/selectors/autocomplete.test.js b/app/selectors/autocomplete.test.js
index 84222998c..2d6202b21 100644
--- a/app/selectors/autocomplete.test.js
+++ b/app/selectors/autocomplete.test.js
@@ -24,6 +24,7 @@ describe('Selectors.Autocomplete', () => {
                 ['@Username', 'username'],
                 ['@USERNAME', 'username'],
                 ['not a match', null],
+                ['@with space', 'with space'],
             ];
 
             testCases.forEach((testCase) => {
@@ -98,6 +99,9 @@ describe('Selectors.Autocomplete', () => {
 
         profiles = filterMembersNotInChannel(state, 'example');
         expect(profiles.length).toBe(2);
+
+        profiles = filterMembersNotInChannel(state, 'test u');
+        expect(profiles.length).toBe(1);
     });
 
     it('Should return profiles in channel', () => {
@@ -136,6 +140,9 @@ describe('Selectors.Autocomplete', () => {
 
         profiles = filterMembersInChannel(state, 'example');
         expect(profiles.length).toBe(2);
+
+        profiles = filterMembersInChannel(state, 'test u');
+        expect(profiles.length).toBe(1);
     });
 
     it('Should return DMs', () => {
diff --git a/detox/e2e/test/autocomplete/at_mention.e2e.js b/detox/e2e/test/autocomplete/at_mention.e2e.js
new file mode 100644
index 000000000..9f7582782
--- /dev/null
+++ b/detox/e2e/test/autocomplete/at_mention.e2e.js
@@ -0,0 +1,167 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+// *******************************************************************
+// - [#] indicates a test step (e.g. # Go to a screen)
+// - [*] indicates an assertion (e.g. * Check the title)
+// - Use element testID when selecting an element. Create one if none.
+// *******************************************************************
+
+import {toChannelScreen} from '@support/ui/screen';
+
+import {Setup} from '@support/server_api';
+
+describe('Autocomplete', () => {
+    let user;
+    let postInput;
+
+    beforeAll(async () => {
+        ({user} = await Setup.apiInit());
+        await toChannelScreen(user);
+    });
+
+    beforeEach(async () => {
+        await device.reloadReactNative();
+
+        // # Select post draft
+        await expect(element(by.id('channel_screen'))).toBeVisible();
+        postInput = await element(by.id('post_input'));
+        await postInput.tap();
+    });
+
+    it('MM-T3409_1 should suggest user based on username', async () => {
+        // # Type "@" to activate at mention autocomplete
+        await expect(element(by.id('autocomplete.at_mention.list'))).not.toExist();
+        await postInput.typeText('@');
+        await expect(element(by.id('autocomplete.at_mention.list'))).toExist();
+
+        // # Type username
+        await postInput.typeText(user.username);
+
+        // * Expect at mention autocomplete to contain associated user suggestion
+        await expect(element(by.id(`autocomplete.at_mention.item.${user.id}`))).toExist();
+    });
+
+    it('MM-T3409_2 should suggest user based on nickname', async () => {
+        // # Type "@" to activate at mention autocomplete
+        await expect(element(by.id('autocomplete.at_mention.list'))).not.toExist();
+        await postInput.typeText('@');
+        await expect(element(by.id('autocomplete.at_mention.list'))).toExist();
+
+        // # Type nickname
+        await postInput.typeText(user.nickname);
+
+        // * Expect at mention autocomplete to contain associated user suggestion
+        await expect(element(by.id(`autocomplete.at_mention.item.${user.id}`))).toExist();
+    });
+
+    it('MM-T3409_3 should suggest user based on first name', async () => {
+        // # Type "@" to activate at mention autocomplete
+        await expect(element(by.id('autocomplete.at_mention.list'))).not.toExist();
+        await postInput.typeText('@');
+        await expect(element(by.id('autocomplete.at_mention.list'))).toExist();
+
+        // # Type first name
+        await postInput.typeText(user.first_name);
+
+        // * Expect at mention autocomplete to contain associated user suggestion
+        await expect(element(by.id(`autocomplete.at_mention.item.${user.id}`))).toExist();
+    });
+
+    it('MM-T3409_4 should suggest user based on last name', async () => {
+        // # Type "@" to activate at mention autocomplete
+        await expect(element(by.id('autocomplete.at_mention.list'))).not.toExist();
+        await postInput.typeText('@');
+        await expect(element(by.id('autocomplete.at_mention.list'))).toExist();
+
+        // # Type last name
+        await postInput.typeText(user.last_name);
+
+        // * Expect at mention autocomplete to contain associated user suggestion
+        await expect(element(by.id(`autocomplete.at_mention.item.${user.id}`))).toExist();
+    });
+
+    it('MM-T3409_5 should suggest user based on lowercase first name', async () => {
+        // # Type "@" to activate at mention autocomplete
+        await expect(element(by.id('autocomplete.at_mention.list'))).not.toExist();
+        await postInput.typeText('@');
+        await expect(element(by.id('autocomplete.at_mention.list'))).toExist();
+
+        // # Type lowercase first name
+        await postInput.typeText(user.first_name.toLowerCase());
+
+        // * Expect at mention autocomplete to contain associated user suggestion
+        await expect(element(by.id(`autocomplete.at_mention.item.${user.id}`))).toExist();
+    });
+
+    it('MM-T3409_6 should suggest user based on lowercase last name', async () => {
+        // # Type "@" to activate at mention autocomplete
+        await expect(element(by.id('autocomplete.at_mention.list'))).not.toExist();
+        await postInput.typeText('@');
+        await expect(element(by.id('autocomplete.at_mention.list'))).toExist();
+
+        // # Type lowercase last name
+        await postInput.typeText(user.last_name.toLowerCase());
+
+        // * Expect at mention autocomplete to contain associated user suggestion
+        await expect(element(by.id(`autocomplete.at_mention.item.${user.id}`))).toExist();
+    });
+
+    it('MM-T3409_7 should suggest user based on full name with space', async () => {
+        // # Type "@" to activate at mention autocomplete
+        await expect(element(by.id('autocomplete.at_mention.list'))).not.toExist();
+        await postInput.typeText('@');
+        await expect(element(by.id('autocomplete.at_mention.list'))).toExist();
+
+        // # Type full name
+        await postInput.typeText(`${user.first_name} ${user.last_name}`);
+
+        // * Expect at mention autocomplete to contain associated user suggestion
+        await expect(element(by.id(`autocomplete.at_mention.item.${user.id}`))).toExist();
+    });
+
+    it('MM-T3409_8 should suggest user based on partial full name with space', async () => {
+        // # Type "@" to activate at mention autocomplete
+        await expect(element(by.id('autocomplete.at_mention.list'))).not.toExist();
+        await postInput.typeText('@');
+        await expect(element(by.id('autocomplete.at_mention.list'))).toExist();
+
+        // # Type partial full name
+        await postInput.typeText(`${user.first_name} ${user.last_name.substring(0, user.last_name.length - 6)}`);
+
+        // * Expect at mention autocomplete to contain associated user suggestion
+        await expect(element(by.id(`autocomplete.at_mention.item.${user.id}`))).toExist();
+    });
+
+    it('MM-T3409_9 should stop suggesting user after full name with trailing space', async () => {
+        // # Type "@" to activate at mention autocomplete
+        await expect(element(by.id('autocomplete.at_mention.list'))).not.toExist();
+        await postInput.typeText('@');
+        await expect(element(by.id('autocomplete.at_mention.list'))).toExist();
+
+        // # Type full name
+        await postInput.typeText(`${user.first_name} ${user.last_name}`);
+
+        // * Expect at mention autocomplete to contain associated user suggestion
+        await expect(element(by.id(`autocomplete.at_mention.item.${user.id}`))).toExist();
+
+        // # Type trailing space
+        await postInput.typeText(' ');
+
+        // * Expect at mention autocomplete not to contain associated user suggestion
+        await expect(element(by.id(`autocomplete.at_mention.item.${user.id}`))).not.toExist();
+    });
+
+    it('MM-T3409_10 should stop suggesting user when keyword is not associated with any user', async () => {
+        // # Type "@" to activate at mention autocomplete
+        await expect(element(by.id('autocomplete.at_mention.list'))).not.toExist();
+        await postInput.typeText('@');
+        await expect(element(by.id('autocomplete.at_mention.list'))).toExist();
+
+        // # Type keyword not associated with any user
+        await postInput.typeText(Date.now().toString());
+
+        // * Expect at mention autocomplete not to contain associated user suggestion
+        await expect(element(by.id(`autocomplete.at_mention.item.${user.id}`))).not.toExist();
+    });
+});