diff --git a/pkg/dev_compiler/tool/ddb b/pkg/dev_compiler/tool/ddb
index 14bd9de9f250..824db4832692 100755
--- a/pkg/dev_compiler/tool/ddb
+++ b/pkg/dev_compiler/tool/ddb
@@ -47,6 +47,11 @@ void main(List<String> args) async {
             'DDC binary. Defaults to false.',
         defaultsTo: false,
         negatable: true)
+    ..addFlag('null-assertions',
+        help: 'Run with assertions that values passed to non-nullable method '
+            'parameters are not null.',
+        defaultsTo: false,
+        negatable: true)
     ..addFlag('observe',
         help:
             'Run the compiler in the Dart VM with --observe. Implies --debug.',
@@ -101,6 +106,7 @@ void main(List<String> args) async {
   var compile = mode == 'compile' || mode == 'all';
   var run = mode == 'run' || mode == 'all';
   var verbose = options['verbose'] as bool;
+  var nonNullAsserts = options['null-assertions'] as bool;
 
   var soundNullSafety = options['sound-null-safety'] as bool;
   // Enable null safety either by passing the `non-nullable` experiment flag or
@@ -272,6 +278,7 @@ void main(List<String> args) async {
     if ($nnbd) {
       sdk.dart.nullSafety($soundNullSafety);
       sdk.dart.weakNullSafetyWarnings(!$soundNullSafety);
+      sdk.dart.nonNullAsserts($nonNullAsserts);
     }
     sdk._debugger.registerDevtoolsFormatter();
     app.$libname.main();
@@ -305,6 +312,7 @@ try {
   if ($nnbd) {
     sdk.dart.nullSafety($soundNullSafety);
     sdk.dart.weakNullSafetyWarnings(!$soundNullSafety);
+    sdk.dart.nonNullAsserts($nonNullAsserts);
   }
   sdk._isolate_helper.startRootIsolate(main, []);
 } catch(e) {
@@ -339,6 +347,7 @@ try {
   if ($nnbd) {
     dart.nullSafety($soundNullSafety);
     dart.weakNullSafetyWarnings(!$soundNullSafety);
+    sdk.dart.nonNullAsserts($nonNullAsserts);
   }
   _isolate_helper.startRootIsolate(() => {}, []);
   main();
diff --git a/pkg/test_runner/lib/src/browser.dart b/pkg/test_runner/lib/src/browser.dart
index 9c8a16a8b263..e9d957a07b56 100644
--- a/pkg/test_runner/lib/src/browser.dart
+++ b/pkg/test_runner/lib/src/browser.dart
@@ -145,9 +145,11 @@ bool _invalidVariableName(String keyword, {bool strictMode = true}) {
 /// or extension, like "math_test". [testNameAlias] is the alias of the
 /// test variable used for import/export (usually relative to its module root).
 /// [testJSDir] is the relative path to the build directory where the
-/// dartdevc-generated JS file is stored.
+/// dartdevc-generated JS file is stored. [nonNullAsserts] enables non-null
+/// assertions for non-nullable method parameters when running with weak null
+/// safety.
 String dartdevcHtml(String testName, String testNameAlias, String testJSDir,
-    Compiler compiler, NnbdMode mode) {
+    Compiler compiler, NnbdMode mode, bool nonNullAsserts) {
   var testId = pathToJSIdentifier(testName);
   var testIdAlias = pathToJSIdentifier(testNameAlias);
   var isKernel = compiler == Compiler.dartdevk;
@@ -234,6 +236,7 @@ requirejs(["$testName", "dart_sdk", "async_helper"],
   if ($isNnbd) {
     sdk.dart.nullSafety($isNnbdStrong);
     sdk.dart.weakNullSafetyWarnings(!$isNnbdStrong);
+    sdk.dart.nonNullAsserts($nonNullAsserts);
   }
 
   dartMainRunner(function testMainWrapper() {
diff --git a/pkg/test_runner/lib/src/compiler_configuration.dart b/pkg/test_runner/lib/src/compiler_configuration.dart
index 03ff44642844..02d7b2a056e6 100644
--- a/pkg/test_runner/lib/src/compiler_configuration.dart
+++ b/pkg/test_runner/lib/src/compiler_configuration.dart
@@ -419,8 +419,12 @@ class Dart2jsCompilerConfiguration extends Dart2xCompilerConfiguration {
 
   List<String> computeCompilerArguments(
       TestFile testFile, List<String> vmOptions, List<String> args) {
+    // TODO(#42403) Handle this option if dart2js supports non-nullable asserts
+    // on non-nullable method arguments.
+    var options = testFile.sharedOptions.toList();
+    options.remove('--null-assertions');
     return [
-      ...testFile.sharedOptions,
+      ...options,
       ..._configuration.sharedOptions,
       ..._experimentsArgument(_configuration, testFile),
       ...testFile.dart2jsOptions,
@@ -510,6 +514,11 @@ class DevCompilerConfiguration extends CompilerConfiguration {
   Command _createCommand(String inputFile, String outputFile,
       List<String> sharedOptions, Map<String, String> environment) {
     var args = <String>[];
+    // Remove option for generating non-null assertions for non-nullable
+    // method parameters in weak mode. DDC treats this as a runtime flag for
+    // the bootstrapping code, instead of a compiler option.
+    var options = sharedOptions.toList();
+    options.remove('--null-assertions');
     if (!_useSdk) {
       // If we're testing a built SDK, DDC will find its own summary.
       //
@@ -524,7 +533,7 @@ class DevCompilerConfiguration extends CompilerConfiguration {
           .toNativePath();
       args.addAll(["--dart-sdk-summary", sdkSummary]);
     }
-    args.addAll(sharedOptions);
+    args.addAll(options);
     args.addAll(_configuration.sharedOptions);
 
     args.addAll([
@@ -1179,8 +1188,12 @@ class FastaCompilerConfiguration extends CompilerConfiguration {
   @override
   List<String> computeCompilerArguments(
       TestFile testFile, List<String> vmOptions, List<String> args) {
+    // Remove shared option for generating non-null assertions for non-nullable
+    // method parameters in weak mode. It's currently unused by the front end.
+    var options = testFile.sharedOptions.toList();
+    options.remove('--null-assertions');
     var arguments = [
-      ...testFile.sharedOptions,
+      ...options,
       ..._configuration.sharedOptions,
       ..._experimentsArgument(_configuration, testFile),
       if (_configuration.configuration.nnbdMode == NnbdMode.strong) ...[
diff --git a/pkg/test_runner/lib/src/test_suite.dart b/pkg/test_runner/lib/src/test_suite.dart
index f1aa7b715d46..fe5f5d2a080f 100644
--- a/pkg/test_runner/lib/src/test_suite.dart
+++ b/pkg/test_runner/lib/src/test_suite.dart
@@ -810,8 +810,10 @@ class StandardTestSuite extends TestSuite {
             "${nameFromModuleRoot.directoryPath}/$nameNoExt";
         var jsDir =
             Path(compilationTempDir).relativeTo(Repository.dir).toString();
+        var nullAssertions =
+            testFile.sharedOptions.contains('--null-assertions');
         content = dartdevcHtml(nameNoExt, nameFromModuleRootNoExt, jsDir,
-            configuration.compiler, configuration.nnbdMode);
+            configuration.compiler, configuration.nnbdMode, nullAssertions);
       }
     }
 
diff --git a/sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/errors.dart b/sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/errors.dart
index ba418a468056..0a3c9a25350a 100644
--- a/sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/errors.dart
+++ b/sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/errors.dart
@@ -28,20 +28,19 @@ final _nullFailedSet = JS('!', 'new Set()');
 // Run-time null safety assertion per:
 // https://github.com/dart-lang/language/blob/master/accepted/future-releases/nnbd/feature-specification.md#automatic-debug-assertion-insertion
 nullFailed(String? fileUri, int? line, int? column, String? variable) {
-  if (strictNullSafety) {
+  if (_nonNullAsserts) {
     throw AssertionErrorImpl(
         'A null value was passed into a non-nullable parameter $variable',
         fileUri,
         line,
         column,
         '$variable != null');
-  } else {
-    var key = '$fileUri:$line:$column';
-    if (!JS('!', '#.has(#)', _nullFailedSet, key)) {
-      JS('', '#.add(#)', _nullFailedSet, key);
-      _nullWarn(
-          'A null value was passed into a non-nullable parameter $variable');
-    }
+  }
+  var key = '$fileUri:$line:$column';
+  if (!JS('!', '#.has(#)', _nullFailedSet, key)) {
+    JS('', '#.add(#)', _nullFailedSet, key);
+    _nullWarn(
+        'A null value was passed into a non-nullable parameter $variable');
   }
 }
 
diff --git a/sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/types.dart b/sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/types.dart
index a4bcaf833278..9a2b72f24680 100644
--- a/sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/types.dart
+++ b/sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/types.dart
@@ -45,6 +45,18 @@ void weakNullSafetyWarnings(bool showWarnings) {
   _weakNullSafetyWarnings = showWarnings;
 }
 
+@notNull
+bool _nonNullAsserts = false;
+
+/// Sets the runtime mode to insert non-null assertions on non-nullable method
+/// parameters.
+///
+/// When [weakNullSafetyWarnings] is also `true` the assertions will fail
+/// instead of printing a warning for the non-null parameters.
+void nonNullAsserts(bool enable) {
+  _nonNullAsserts = enable;
+}
+
 final metadata = JS('', 'Symbol("metadata")');
 
 /// Types in dart are represented internally at runtime as follows.
diff --git a/tests/language/nnbd/null_assertions/parameter_checks_test.dart b/tests/language/nnbd/null_assertions/parameter_checks_test.dart
index c6f9cc64aec8..d841cd44ff14 100644
--- a/tests/language/nnbd/null_assertions/parameter_checks_test.dart
+++ b/tests/language/nnbd/null_assertions/parameter_checks_test.dart
@@ -5,7 +5,8 @@
 // Test for null assertions for parameters in NNBD weak mode.
 
 // Requirements=nnbd-weak
-// VMOptions=--enable-asserts --null-assertions
+// VMOptions=--enable-asserts
+// SharedOptions=--null-assertions
 
 // Opt out of Null Safety:
 // @dart = 2.6