diff --git a/app/assets/javascripts/diffs/stores/legacy_diffs/actions.js b/app/assets/javascripts/diffs/stores/legacy_diffs/actions.js
index 14db30db975141afc7a0448ed549de940a28fa17..17e6f378fa2532c2d86b9c79a3a3b8e1a1e4fc3e 100644
--- a/app/assets/javascripts/diffs/stores/legacy_diffs/actions.js
+++ b/app/assets/javascripts/diffs/stores/legacy_diffs/actions.js
@@ -59,6 +59,7 @@ import {
   EVT_MR_PREPARED,
   FILE_DIFF_POSITION_TYPE,
   EVT_DISCUSSIONS_ASSIGNED,
+  OLD_LINE_TYPE,
 } from '../../constants';
 import {
   DISCUSSION_SINGLE_DIFF_FAILED,
@@ -662,6 +663,48 @@ export async function saveDiffDiscussion({ note, formData }) {
     });
 }
 
+export function getLinesForDiscussion({ discussion }) {
+  const lines = [];
+
+  if (!discussion?.diff_file || !discussion?.position) {
+    return lines;
+  }
+
+  const diffFile = this.diffFiles.find((file) => file.file_hash === discussion.diff_file.file_hash);
+
+  if (!diffFile) {
+    return lines;
+  }
+
+  const diffLines = diffFile[INLINE_DIFF_LINES_KEY];
+  let isAdding = false;
+  const { start, end } = discussion.position?.line_range || {};
+
+  if (!start || !end) {
+    return lines;
+  }
+
+  for (let i = 0, diffLinesLength = diffLines.length - 1; i <= diffLinesLength; i += 1) {
+    const line = diffLines[i];
+
+    if (start.line_code === line.line_code) {
+      isAdding = true;
+    }
+
+    if (isAdding) {
+      if (line.type !== OLD_LINE_TYPE) {
+        lines.push(line);
+      }
+
+      if (end.line_code === line.line_code) {
+        break;
+      }
+    }
+  }
+
+  return lines;
+}
+
 export function toggleTreeOpen(path) {
   this[types.TOGGLE_FOLDER_OPEN](path);
 }
diff --git a/spec/frontend/diffs/stores/legacy_diffs/actions_spec.js b/spec/frontend/diffs/stores/legacy_diffs/actions_spec.js
index 57f6fe18ea37f322d9539645d762a34b232456d7..22580b98e7c3e31f1aed2069c9b12cf889ae3e0e 100644
--- a/spec/frontend/diffs/stores/legacy_diffs/actions_spec.js
+++ b/spec/frontend/diffs/stores/legacy_diffs/actions_spec.js
@@ -9,9 +9,11 @@ import { getDiffFileMock } from 'jest/diffs/mock_data/diff_file';
 import {
   DIFF_VIEW_COOKIE_NAME,
   INLINE_DIFF_VIEW_TYPE,
+  INLINE_DIFF_LINES_KEY,
   PARALLEL_DIFF_VIEW_TYPE,
   EVT_MR_PREPARED,
   FILE_DIFF_POSITION_TYPE,
+  OLD_LINE_TYPE,
 } from '~/diffs/constants';
 import {
   BUILDING_YOUR_MR,
@@ -1321,6 +1323,137 @@ describe('legacyDiffs actions', () => {
     });
   });
 
+  describe('getLinesForDiscussion', () => {
+    it('returns empty array when discussion is null or undefined', () => {
+      expect(store.getLinesForDiscussion({ discussion: null })).toEqual([]);
+      expect(store.getLinesForDiscussion({ discussion: undefined })).toEqual([]);
+    });
+
+    it('returns empty array when discussion has no position', () => {
+      const result = store.getLinesForDiscussion({ discussion: {} });
+      expect(result).toEqual([]);
+    });
+
+    it('returns empty array when line_range is missing', () => {
+      const discussion = { position: {} };
+      const result = store.getLinesForDiscussion({ discussion });
+      expect(result).toEqual([]);
+    });
+
+    it('returns empty array when diffFile is not found', () => {
+      const discussion = {
+        diff_file: { file_hash: 'nonexistent_hash' },
+        position: {
+          line_range: {
+            start: { line_code: 'start_line' },
+            end: { line_code: 'end_line' },
+          },
+        },
+      };
+
+      store.diffFiles = [{ file_hash: 'different_hash' }];
+
+      const result = store.getLinesForDiscussion({ discussion });
+      expect(result).toEqual([]);
+    });
+
+    it('returns correct lines for a valid discussion', () => {
+      const diffLines = [
+        { line_code: 'line1', type: 'new' },
+        { line_code: 'line2', type: 'new' },
+        { line_code: 'line3', type: 'new' },
+        { line_code: 'line4', type: 'new' },
+        { line_code: 'line5', type: 'new' },
+      ];
+
+      const diffFile = {
+        file_hash: 'abc123',
+        [INLINE_DIFF_LINES_KEY]: diffLines,
+      };
+
+      const discussion = {
+        diff_file: { file_hash: 'abc123' },
+        position: {
+          line_range: {
+            start: { line_code: 'line2' },
+            end: { line_code: 'line4' },
+          },
+        },
+      };
+
+      store.diffFiles = [diffFile];
+
+      const result = store.getLinesForDiscussion({ discussion });
+      expect(result).toEqual([
+        { line_code: 'line2', type: 'new' },
+        { line_code: 'line3', type: 'new' },
+        { line_code: 'line4', type: 'new' },
+      ]);
+    });
+
+    it('excludes old lines from the result', () => {
+      const diffLines = [
+        { line_code: 'line1', type: 'new' },
+        { line_code: 'line2', type: OLD_LINE_TYPE },
+        { line_code: 'line3', type: 'new' },
+        { line_code: 'line4', type: OLD_LINE_TYPE },
+        { line_code: 'line5', type: 'new' },
+      ];
+
+      const diffFile = {
+        file_hash: 'abc123',
+        [INLINE_DIFF_LINES_KEY]: diffLines,
+      };
+
+      const discussion = {
+        diff_file: { file_hash: 'abc123' },
+        position: {
+          line_range: {
+            start: { line_code: 'line1' },
+            end: { line_code: 'line5' },
+          },
+        },
+      };
+
+      store.diffFiles = [diffFile];
+
+      const result = store.getLinesForDiscussion({ discussion });
+      expect(result).toEqual([
+        { line_code: 'line1', type: 'new' },
+        { line_code: 'line3', type: 'new' },
+        { line_code: 'line5', type: 'new' },
+      ]);
+    });
+
+    it('handles case when start and end are the same line', () => {
+      const diffLines = [
+        { line_code: 'line1', type: 'new' },
+        { line_code: 'line2', type: 'new' },
+        { line_code: 'line3', type: 'new' },
+      ];
+
+      const diffFile = {
+        file_hash: 'abc123',
+        [INLINE_DIFF_LINES_KEY]: diffLines,
+      };
+
+      const discussion = {
+        diff_file: { file_hash: 'abc123' },
+        position: {
+          line_range: {
+            start: { line_code: 'line2' },
+            end: { line_code: 'line2' },
+          },
+        },
+      };
+
+      store.diffFiles = [diffFile];
+
+      const result = store.getLinesForDiscussion({ discussion });
+      expect(result).toEqual([{ line_code: 'line2', type: 'new' }]);
+    });
+  });
+
   describe('toggleTreeOpen', () => {
     it('commits TOGGLE_FOLDER_OPEN', () => {
       return testAction(