diff --git a/e2e-tests/cypress/tests/integration/channels/collapsed_reply_threads/replies_spec.js b/e2e-tests/cypress/tests/integration/channels/collapsed_reply_threads/replies_spec.js
index 16b30acf5b..6d7c252bfe 100644
--- a/e2e-tests/cypress/tests/integration/channels/collapsed_reply_threads/replies_spec.js
+++ b/e2e-tests/cypress/tests/integration/channels/collapsed_reply_threads/replies_spec.js
@@ -10,6 +10,8 @@
 // Stage: @prod
 // Group: @channels @collapsed_reply_threads
 
+import * as TIMEOUTS from '../../../fixtures/timeouts';
+
 describe('Collapsed Reply Threads', () => {
     let testTeam;
     let testUser;
@@ -174,4 +176,45 @@ describe('Collapsed Reply Threads', () => {
             cy.uiCloseRHS();
         });
     });
+
+    it('MM-T5413 should auto-scroll to bottom upon pasting long text in reply', () => {
+        // # Post a root post as current user
+        cy.postMessageAs({
+            sender: testUser,
+            message: 'Another interesting post,',
+            channelId: testChannel.id,
+        }).then(({id: rootId}) => {
+            // # Post multiple replies as other user so that the new messages line is pushed up
+            Cypress._.times(20, (i) => {
+                cy.postMessageAs({
+                    sender: otherUser,
+                    message: 'Reply ' + i,
+                    channelId: testChannel.id,
+                    rootId,
+                });
+            });
+
+            // # Click root post
+            cy.get(`#post_${rootId}`).click();
+
+            // # Wait for RHS to open and scroll to position
+            cy.wait(TIMEOUTS.ONE_SEC);
+
+            // * RHS should open and the editor's actions should not be visible.
+            cy.get('#rhsContainer').findByTestId('SendMessageButton').should('not.be.visible');
+
+            // # Close RHS
+            cy.uiCloseRHS();
+
+            // # Click root post
+            cy.get(`#post_${rootId}`).click();
+
+            // # Paste a multiline string in the RHS textbox.
+            const text = 'word '.repeat(2000);
+            cy.get('#rhsContainer').findByTestId('reply_textbox').clear().invoke('val', text).trigger('input');
+
+            // * RHS should open and the editor should be visible and focused
+            cy.get('#rhsContainer').findByTestId('SendMessageButton').should('be.visible');
+        });
+    });
 });
diff --git a/webapp/channels/src/components/advanced_text_editor/advanced_text_editor.tsx b/webapp/channels/src/components/advanced_text_editor/advanced_text_editor.tsx
index b3c683c4a2..9b76d8bd7a 100644
--- a/webapp/channels/src/components/advanced_text_editor/advanced_text_editor.tsx
+++ b/webapp/channels/src/components/advanced_text_editor/advanced_text_editor.tsx
@@ -131,7 +131,7 @@ const AdvanceTextEditor = ({
     canUploadFiles,
     enableEmojiPicker,
     enableGifPicker,
-    handleBlur,
+    handleBlur: onBlur,
     handlePostError,
     emitTypingEvent,
     handleMouseUpKeyUp,
@@ -170,6 +170,7 @@ const AdvanceTextEditor = ({
     const [scrollbarWidth, setScrollbarWidth] = useState(0);
     const [renderScrollbar, setRenderScrollbar] = useState(false);
     const [showFormattingSpacer, setShowFormattingSpacer] = useState(shouldShowPreview);
+    const [keepEditorInFocus, setKeepEditorInFocus] = useState(false);
 
     const input = textboxRef.current?.getInputBox();
 
@@ -187,6 +188,15 @@ const AdvanceTextEditor = ({
         setShowPreview(!shouldShowPreview);
     }, [shouldShowPreview, setShowPreview]);
 
+    const handleBlur = useCallback(() => {
+        onBlur?.();
+        setKeepEditorInFocus(false);
+    }, [onBlur]);
+
+    const handleFocus = useCallback(() => {
+        setKeepEditorInFocus(true);
+    }, []);
+
     let serverErrorJsx = null;
     if (serverError) {
         serverErrorJsx = (
@@ -422,6 +432,7 @@ const AdvanceTextEditor = ({
                 />
             )}
             slot2={null}
+            shouldScrollIntoView={keepEditorInFocus}
         />
     );
 
@@ -479,6 +490,7 @@ const AdvanceTextEditor = ({
                             handlePostError={handlePostError}
                             value={messageValue}
                             onBlur={handleBlur}
+                            onFocus={handleFocus}
                             emojiEnabled={enableEmojiPicker}
                             createMessage={createMessage}
                             channelId={channelId}
diff --git a/webapp/channels/src/components/textbox/textbox.tsx b/webapp/channels/src/components/textbox/textbox.tsx
index dc89524e21..1ba345a75e 100644
--- a/webapp/channels/src/components/textbox/textbox.tsx
+++ b/webapp/channels/src/components/textbox/textbox.tsx
@@ -44,6 +44,7 @@ export type Props = {
     onMouseUp?: (e: React.MouseEvent<TextboxElement>) => void;
     onKeyUp?: (e: React.KeyboardEvent<TextboxElement>) => void;
     onBlur?: (e: FocusEvent<TextboxElement>) => void;
+    onFocus?: (e: FocusEvent<TextboxElement>) => void;
     supportsCommands?: boolean;
     handlePostError?: (message: JSX.Element | null) => void;
     onPaste?: (e: ClipboardEvent) => void;
@@ -312,6 +313,7 @@ export default class Textbox extends React.PureComponent<Props> {
                     onKeyUp={this.handleKeyUp}
                     onComposition={this.props.onComposition}
                     onBlur={this.handleBlur}
+                    onFocus={this.props.onFocus}
                     onHeightChange={this.props.onHeightChange}
                     onWidthChange={this.props.onWidthChange}
                     onPaste={this.props.onPaste}