diff --git a/packages/angular/build/src/builders/unit-test/runners/vitest/executor.ts b/packages/angular/build/src/builders/unit-test/runners/vitest/executor.ts
index ed754d9f9c30..39584a5844f0 100644
--- a/packages/angular/build/src/builders/unit-test/runners/vitest/executor.ts
+++ b/packages/angular/build/src/builders/unit-test/runners/vitest/executor.ts
@@ -85,6 +85,11 @@ export class VitestExecutor implements TestExecutor {
 
     updateExternalMetadata(buildResult, this.externalMetadata, undefined, true);
 
+    // Reset the exit code to allow for a clean state.
+    // This is necessary because Vitest may set the exit code on failure, which can
+    // affect subsequent runs in watch mode or when running multiple builders.
+    process.exitCode = 0;
+
     // Initialize Vitest if not already present.
     this.vitest ??= await this.initializeVitest();
     const vitest = this.vitest;
@@ -122,7 +127,17 @@ export class VitestExecutor implements TestExecutor {
     // Check if all the tests pass to calculate the result
     const testModules = testResults?.testModules ?? this.vitest.state.getTestModules();
 
-    yield { success: testModules.every((testModule) => testModule.ok()) };
+    let success = testModules.every((testModule) => testModule.ok());
+    // Vitest does not return a failure result when coverage thresholds are not met.
+    // Instead, it sets the process exit code to 1.
+    // We check this exit code to determine if the test run should be considered a failure.
+    if (success && process.exitCode === 1) {
+      success = false;
+      // Reset the exit code to prevent it from carrying over to subsequent runs/builds
+      process.exitCode = 0;
+    }
+
+    yield { success };
   }
 
   async [Symbol.asyncDispose](): Promise<void> {
diff --git a/packages/angular/build/src/builders/unit-test/runners/vitest/plugins.ts b/packages/angular/build/src/builders/unit-test/runners/vitest/plugins.ts
index 4bd6666250e7..39d42c62d05d 100644
--- a/packages/angular/build/src/builders/unit-test/runners/vitest/plugins.ts
+++ b/packages/angular/build/src/builders/unit-test/runners/vitest/plugins.ts
@@ -370,8 +370,16 @@ async function generateCoverageOption(
     ...(optionsCoverage.include
       ? { include: ['spec-*.js', 'chunk-*.js', ...optionsCoverage.include] }
       : {}),
-    thresholds: optionsCoverage.thresholds,
-    watermarks: optionsCoverage.watermarks,
+    // The 'in' operator is used here because 'configCoverage' is a union type and
+    // not all coverage providers support thresholds or watermarks.
+    thresholds: mergeCoverageObjects(
+      configCoverage && 'thresholds' in configCoverage ? configCoverage.thresholds : undefined,
+      optionsCoverage.thresholds,
+    ),
+    watermarks: mergeCoverageObjects(
+      configCoverage && 'watermarks' in configCoverage ? configCoverage.watermarks : undefined,
+      optionsCoverage.watermarks,
+    ),
     // Special handling for `exclude`/`reporters` due to an undefined value causing upstream failures
     ...(optionsCoverage.exclude
       ? {
@@ -388,3 +396,26 @@ async function generateCoverageOption(
       : {}),
   };
 }
+
+/**
+ * Merges coverage related objects while ignoring any `undefined` values.
+ * This ensures that Angular CLI options correctly override Vitest configuration
+ * only when explicitly provided.
+ */
+function mergeCoverageObjects<T extends object>(
+  configValue: T | undefined,
+  optionsValue: T | undefined,
+): T | undefined {
+  if (optionsValue === undefined) {
+    return configValue;
+  }
+
+  const result: Record<string, unknown> = { ...(configValue ?? {}) };
+  for (const [key, value] of Object.entries(optionsValue)) {
+    if (value !== undefined) {
+      result[key] = value;
+    }
+  }
+
+  return Object.keys(result).length > 0 ? (result as T) : undefined;
+}
diff --git a/packages/angular/build/src/builders/unit-test/tests/options/runner-config-coverage_spec.ts b/packages/angular/build/src/builders/unit-test/tests/options/runner-config-coverage_spec.ts
new file mode 100644
index 000000000000..c46c38da79ad
--- /dev/null
+++ b/packages/angular/build/src/builders/unit-test/tests/options/runner-config-coverage_spec.ts
@@ -0,0 +1,120 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.dev/license
+ */
+
+import { execute } from '../../index';
+import {
+  BASE_OPTIONS,
+  describeBuilder,
+  UNIT_TEST_BUILDER_INFO,
+  setupApplicationTarget,
+} from '../setup';
+
+describeBuilder(execute, UNIT_TEST_BUILDER_INFO, (harness) => {
+  describe('Option: "runnerConfig" Coverage Merging', () => {
+    beforeEach(() => {
+      setupApplicationTarget(harness);
+    });
+
+    describe('Vitest Runner', () => {
+      it('should preserve thresholds from Vitest config when not overridden by CLI', async () => {
+        harness.writeFile(
+          'vitest-base.config.ts',
+          `
+          import { defineConfig } from 'vitest/config';
+          export default defineConfig({
+            test: {
+              coverage: {
+                thresholds: {
+                  branches: 100
+                }
+              }
+            }
+          });
+        `,
+        );
+
+        harness.useTarget('test', {
+          ...BASE_OPTIONS,
+          runnerConfig: true,
+          coverage: true,
+        });
+
+        const { result } = await harness.executeOnce();
+
+        // Should fail because branches are not 100%
+        expect(result?.success).toBeFalse();
+      });
+
+      it('should override Vitest config thresholds with CLI thresholds', async () => {
+        harness.writeFile(
+          'vitest-base.config.ts',
+          `
+          import { defineConfig } from 'vitest/config';
+          export default defineConfig({
+            test: {
+              coverage: {
+                thresholds: {
+                  branches: 100
+                }
+              }
+            }
+          });
+        `,
+        );
+
+        harness.useTarget('test', {
+          ...BASE_OPTIONS,
+          runnerConfig: true,
+          coverage: true,
+          coverageThresholds: {
+            branches: 0,
+          },
+        });
+
+        const { result } = await harness.executeOnce();
+
+        // Should pass because CLI overrides threshold to 0
+        expect(result?.success).toBeTrue();
+      });
+
+      it('should merge partial CLI thresholds with Vitest config thresholds', async () => {
+        harness.writeFile(
+          'vitest-base.config.ts',
+          `
+          import { defineConfig } from 'vitest/config';
+          export default defineConfig({
+            test: {
+              coverage: {
+                thresholds: {
+                  statements: 100,
+                  branches: 100
+                }
+              }
+            }
+          });
+        `,
+        );
+
+        harness.useTarget('test', {
+          ...BASE_OPTIONS,
+          runnerConfig: true,
+          coverage: true,
+          coverageThresholds: {
+            statements: 0,
+            // branches is undefined here, should remain 100 from config
+          },
+        });
+
+        const { result } = await harness.executeOnce();
+
+        // Should still fail because branches threshold (100) is not met
+        expect(result?.success).toBeFalse();
+      });
+    });
+  });
+});