diff --git a/packages/typescript-estree/src/parseSettings/getProjectConfigFiles.ts b/packages/typescript-estree/src/parseSettings/getProjectConfigFiles.ts
index f7f3dc8851b8..dff7be7412ec 100644
--- a/packages/typescript-estree/src/parseSettings/getProjectConfigFiles.ts
+++ b/packages/typescript-estree/src/parseSettings/getProjectConfigFiles.ts
@@ -39,6 +39,12 @@ export function getProjectConfigFiles(
   let directory = path.dirname(parseSettings.filePath);
   const checkedDirectories = [directory];
 
+  // Normalize tsconfigRootDir once to avoid repeated regex operations in the loop
+  const normalizedTsconfigRootDirLength = Math.max(
+    1,
+    parseSettings.tsconfigRootDir.replace(/[/\\]+$/, '').length,
+  );
+
   do {
     log('Checking tsconfig.json path: %s', directory);
     const tsconfigPath = path.join(directory, 'tsconfig.json');
@@ -57,7 +63,7 @@ export function getProjectConfigFiles(
     checkedDirectories.push(directory);
   } while (
     directory.length > 1 &&
-    directory.length >= parseSettings.tsconfigRootDir.length
+    directory.length >= normalizedTsconfigRootDirLength
   );
 
   throw new Error(
diff --git a/packages/typescript-estree/tests/lib/getProjectConfigFiles.test.ts b/packages/typescript-estree/tests/lib/getProjectConfigFiles.test.ts
index 8e464eb746fc..6762dce3e67c 100644
--- a/packages/typescript-estree/tests/lib/getProjectConfigFiles.test.ts
+++ b/packages/typescript-estree/tests/lib/getProjectConfigFiles.test.ts
@@ -178,5 +178,20 @@ describe(getProjectConfigFiles, () => {
         `[Error: project was set to \`true\` but couldn't find any tsconfig.json relative to './repos/repo/packages/package/file.ts' within '/'.]`,
       );
     });
+
+    it('works correctly with trailing path separator in tsconfigRootDir', () => {
+      mockExistsSync.mockImplementation(
+        filePath => filePath === path.normalize('repos/repo/tsconfig.json'),
+      );
+
+      const actual = getProjectConfigFiles(
+        { ...parseSettings, tsconfigRootDir: './repos/repo/' },
+        true,
+      );
+
+      expect(actual).toStrictEqual([
+        path.normalize('repos/repo/tsconfig.json'),
+      ]);
+    });
   });
 });