@@ -232,6 +232,8 @@ function updateProjects(tree: Tree, context: SchematicContext) {
 
 // Use @angular/build directly if there is no devkit package usage
 if (!hasAngularDevkitUsage) {
+const karmaConfigFiles = new Set<string>();
+
 for (const [, target] of allWorkspaceTargets(workspace)) {
 switch (target.builder) {
 case Builders.Application:
@@ -245,9 +247,15 @@ function updateProjects(tree: Tree, context: SchematicContext) {
 break;
 case Builders.Karma:
 target.builder = '@angular/build:karma';
-// Remove "builderMode" option since the builder will always use "application"
 for (const [, karmaOptions] of allTargetOptions(target)) {
+// Remove "builderMode" option since the builder will always use "application"
 delete karmaOptions['builderMode'];
+
+// Collect custom karma configurations for @angular-devkit/build-angular plugin removal
+const karmaConfig = karmaOptions['karmaConfig'];
+if (karmaConfig && typeof karmaConfig === 'string') {
+karmaConfigFiles.add(karmaConfig);
+}
 }
 break;
 case Builders.NgPackagr:
@@ -292,6 +300,34 @@ function updateProjects(tree: Tree, context: SchematicContext) {
 }),
 );
 }
+
+for (const karmaConfigFile of karmaConfigFiles) {
+if (!tree.exists(karmaConfigFile)) {
+continue;
+}
+
+try {
+const originalKarmaConfigText = tree.readText(karmaConfigFile);
+const updatedKarmaConfigText = originalKarmaConfigText
+.replaceAll(`require('@angular-devkit/build-angular/plugins/karma'),`, '')
+.replaceAll(`require('@angular-devkit/build-angular/plugins/karma')`, '');
+
+if (updatedKarmaConfigText.includes('@angular-devkit/build-angular/plugins')) {
+throw new Error(
+'Migration does not support found usage of "@angular-devkit/build-angular".',
+);
+} else {
+tree.overwrite(karmaConfigFile, updatedKarmaConfigText);
+}
+} catch (error) {
+const reason = error instanceof Error ? `Reason: ${error.message}` : '';
+context.logger.warn(
+`Unable to update custom karma configuration file ("${karmaConfigFile}"). ` +
+reason +
+'\nReferences to the "@angular-devkit/build-angular" package within the file may need to be removed manually.',
+);
+}
+}
 }
 
 return chain(rules);

@@ -130,6 +130,103 @@ describe(`Migration to use the application builder`, () => {
 expect(builderMode).toBeUndefined();
 });
 
+it(`should update file for 'karmaConfig' karma option (no require trailing comma)`, async () => {
+addWorkspaceTarget(tree, 'test', {
+'builder': Builders.Karma,
+'options': {
+'karmaConfig': './karma.conf.js',
+'polyfills': ['zone.js', 'zone.js/testing'],
+'tsConfig': 'projects/app-a/tsconfig.spec.json',
+},
+});
+tree.create(
+'./karma.conf.js',
+`
+module.exports = function (config) {
+config.set({
+basePath: '',
+frameworks: ['jasmine', '@angular-devkit/build-angular'],
+plugins: [
+require('karma-jasmine'),
+require('karma-chrome-launcher'),
+require('karma-jasmine-html-reporter'),
+require('karma-coverage'),
+require('@angular-devkit/build-angular/plugins/karma')
+]
+});
+};`,
+);
+
+const newTree = await schematicRunner.runSchematic(schematicName, {}, tree);
+const {
+projects: { app },
+} = JSON.parse(newTree.readContent('/angular.json'));
+
+const { karmaConfig } = app.architect['test'].options;
+expect(karmaConfig).toBe('./karma.conf.js');
+
+const karmaConfigText = newTree.readText('./karma.conf.js');
+expect(karmaConfigText).not.toContain(`require('@angular-devkit/build-angular/plugins/karma')`);
+});
+
+it(`should update file for 'karmaConfig' karma option (require trailing comma)`, async () => {
+addWorkspaceTarget(tree, 'test', {
+'builder': Builders.Karma,
+'options': {
+'karmaConfig': './karma.conf.js',
+'polyfills': ['zone.js', 'zone.js/testing'],
+'tsConfig': 'projects/app-a/tsconfig.spec.json',
+},
+});
+tree.create(
+'./karma.conf.js',
+`
+module.exports = function (config) {
+config.set({
+basePath: '',
+frameworks: ['jasmine', '@angular-devkit/build-angular'],
+plugins: [
+require('karma-jasmine'),
+require('karma-chrome-launcher'),
+require('karma-jasmine-html-reporter'),
+require('karma-coverage'),
+require('@angular-devkit/build-angular/plugins/karma'),
+]
+});
+};`,
+);
+
+const newTree = await schematicRunner.runSchematic(schematicName, {}, tree);
+const {
+projects: { app },
+} = JSON.parse(newTree.readContent('/angular.json'));
+
+const { karmaConfig } = app.architect['test'].options;
+expect(karmaConfig).toBe('./karma.conf.js');
+
+const karmaConfigText = newTree.readText('./karma.conf.js');
+expect(karmaConfigText).not.toContain(`require('@angular-devkit/build-angular/plugins/karma')`);
+});
+
+it(`should ignore missing file for 'karmaConfig' karma option`, async () => {
+addWorkspaceTarget(tree, 'test', {
+'builder': Builders.Karma,
+'options': {
+'karmaConfig': './karma.conf.js',
+'polyfills': ['zone.js', 'zone.js/testing'],
+'tsConfig': 'projects/app-a/tsconfig.spec.json',
+},
+});
+
+const newTree = await schematicRunner.runSchematic(schematicName, {}, tree);
+const {
+projects: { app },
+} = JSON.parse(newTree.readContent('/angular.json'));
+
+const { karmaConfig } = app.architect['test'].options;
+expect(karmaConfig).toBe('./karma.conf.js');
+});
+
 it('should remove tilde prefix from CSS @import specifiers', async () => {
 // Replace outputPath
 tree.create(