diff --git a/pkgs/jni/lib/jni.dart b/pkgs/jni/lib/jni.dart
index 49ce91ddd8..e5a8d44eec 100644
--- a/pkgs/jni/lib/jni.dart
+++ b/pkgs/jni/lib/jni.dart
@@ -93,3 +93,4 @@ export 'src/lang/lang.dart';
 export 'src/nio/nio.dart';
 export 'src/types.dart' hide JTypeBase, lowestCommonSuperType;
 export 'src/util/util.dart';
+export 'src/converter.dart';
diff --git a/pkgs/jni/lib/src/converter.dart b/pkgs/jni/lib/src/converter.dart
new file mode 100644
index 0000000000..7ca97dc94c
--- /dev/null
+++ b/pkgs/jni/lib/src/converter.dart
@@ -0,0 +1,235 @@
+// Copyright (c) 2025, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'jarray.dart';
+import 'jni.dart';
+import 'jobject.dart';
+import 'lang/lang.dart';
+import 'types.dart';
+import 'util/util.dart';
+
+JObject _defaultJNIConverter(Object o) =>
+    throw UnimplementedError('No conversion for $o');
+
+/// Converts a Dart object to a JNI object.
+JObject? toJObject(
+  Object? dartObject, {
+  JObject Function(Object) convertOther = _defaultJNIConverter,
+}) =>
+    switch (dartObject) {
+      null => null,
+      JObject() => dartObject,
+      bool() => dartObject.toJBoolean(),
+      int() => dartObject.toJLong(),
+      double() => dartObject.toJDouble(),
+      String() => dartObject.toJString(),
+      List<Object?>() => dartObject.toJList(convertOther: convertOther),
+      Set<Object?>() => dartObject.toJSet(convertOther: convertOther),
+      Map<Object?, Object?>() => dartObject.toJMap(convertOther: convertOther),
+      _ => convertOther(dartObject),
+    };
+
+extension DartListToJList on List<Object?> {
+  JList<JObject?> toJList({
+    JObject Function(Object) convertOther = _defaultJNIConverter,
+  }) {
+    final list = JList.array(JObject.nullableType);
+    for (final element in this) {
+      list.add(toJObject(element, convertOther: convertOther));
+    }
+    return list;
+  }
+}
+
+extension DartSetToJSet on Set<Object?> {
+  JSet<JObject?> toJSet({
+    JObject Function(Object) convertOther = _defaultJNIConverter,
+  }) {
+    final set = JSet.hash(JObject.nullableType);
+    for (final element in this) {
+      set.add(toJObject(element, convertOther: convertOther));
+    }
+    return set;
+  }
+}
+
+extension DartMapToJMap on Map<Object?, Object?> {
+  JMap<JObject?, JObject?> toJMap({
+    JObject Function(Object) convertOther = _defaultJNIConverter,
+  }) {
+    final map = JMap.hash(JObject.nullableType, JObject.nullableType);
+    for (final entry in entries) {
+      map[toJObject(entry.key, convertOther: convertOther)] =
+          toJObject(entry.value, convertOther: convertOther);
+    }
+    return map;
+  }
+}
+
+extension DartListToJBooleanArray on List<bool> {
+  JBooleanArray toJBooleanArray() =>
+      JBooleanArray(length)..setRange(0, length, this);
+}
+
+extension DartListToJByteArray on List<int> {
+  JByteArray toJByteArray() => JByteArray(length)..setRange(0, length, this);
+}
+
+extension DartListToJCharArray on List<int> {
+  JCharArray toJCharArray() => JCharArray(length)..setRange(0, length, this);
+}
+
+extension DartListToJShortArray on List<int> {
+  JShortArray toJShortArray() => JShortArray(length)..setRange(0, length, this);
+}
+
+extension DartListToJIntArray on List<int> {
+  JIntArray toJIntArray() => JIntArray(length)..setRange(0, length, this);
+}
+
+extension DartListToJLongArray on List<int> {
+  JLongArray toJLongArray() => JLongArray(length)..setRange(0, length, this);
+}
+
+extension DartListToJFloatArray on List<double> {
+  JFloatArray toJFloatArray() => JFloatArray(length)..setRange(0, length, this);
+}
+
+extension DartListToJDoubleArray on List<double> {
+  JDoubleArray toJDoubleArray() =>
+      JDoubleArray(length)..setRange(0, length, this);
+}
+
+extension DartListToJObjectArray<E extends JObject?> on List<E> {
+  JArray<E> toJObjectArray(JType<E> elementType) =>
+      JArray.of(elementType, this);
+}
+
+Object? _defaultDartConverter(JObject? o) => o;
+
+/// Converts a JNI object to a Dart object.
+Object? toDartObject(
+  JObject? jObject, {
+  Object? Function(JObject?) convertOther = _defaultDartConverter,
+}) {
+  if (jObject == null) return null;
+
+  if (jObject.isA(JString.type)) {
+    return jObject.as(JString.type).toDartString();
+  }
+  if (jObject.isA(JBoolean.type)) {
+    return jObject.as(JBoolean.type).booleanValue();
+  }
+  if (jObject.isA(JInteger.type)) {
+    return jObject.as(JInteger.type).intValue();
+  }
+  if (jObject.isA(JLong.type)) {
+    return jObject.as(JLong.type).longValue();
+  }
+  if (jObject.isA(JDouble.type)) {
+    return jObject.as(JDouble.type).doubleValue();
+  }
+  if (jObject.isA(JFloat.type)) {
+    return jObject.as(JFloat.type).floatValue();
+  }
+  if (jObject.isA(JShort.type)) {
+    return jObject.as(JShort.type).shortValue();
+  }
+  if (jObject.isA(JByte.type)) {
+    return jObject.as(JByte.type).byteValue();
+  }
+  if (jObject.isA(JCharacter.type)) {
+    return jObject.as(JCharacter.type).charValue();
+  }
+
+  if (jObject.isA(JBooleanArray.type)) {
+    return jObject.as(JBooleanArray.type).toList();
+  }
+  if (jObject.isA(JByteArray.type)) {
+    return jObject.as(JByteArray.type).toList();
+  }
+  if (jObject.isA(JCharArray.type)) {
+    return jObject.as(JCharArray.type).toList();
+  }
+  if (jObject.isA(JShortArray.type)) {
+    return jObject.as(JShortArray.type).toList();
+  }
+  if (jObject.isA(JIntArray.type)) {
+    return jObject.as(JIntArray.type).toList();
+  }
+  if (jObject.isA(JLongArray.type)) {
+    return jObject.as(JLongArray.type).toList();
+  }
+  if (jObject.isA(JFloatArray.type)) {
+    return jObject.as(JFloatArray.type).toList();
+  }
+  if (jObject.isA(JDoubleArray.type)) {
+    return jObject.as(JDoubleArray.type).toList();
+  }
+
+  if (jObject.isA(JArray.type(JObject.nullableType))) {
+    return jObject
+        .as(JArray.type(JObject.nullableType))
+        .toDeepDartList(convertOther: convertOther);
+  }
+
+  if (jObject.isA(JList.type(JObject.nullableType))) {
+    return jObject
+        .as(JList.type(JObject.nullableType))
+        .toDeepDartList(convertOther: convertOther);
+  }
+  if (jObject.isA(JSet.type(JObject.nullableType))) {
+    return jObject
+        .as(JSet.type(JObject.nullableType))
+        .toDeepDartSet(convertOther: convertOther);
+  }
+  if (jObject.isA(JMap.type(JObject.nullableType, JObject.nullableType))) {
+    return jObject
+        .as(JMap.type(JObject.nullableType, JObject.nullableType))
+        .toDeepDartMap(convertOther: convertOther);
+  }
+
+  return convertOther(jObject);
+}
+
+Object? toNullableDartObject(
+  JObject? jObject, {
+  Object? Function(JObject?) convertOther = _defaultDartConverter,
+}) =>
+    toDartObject(jObject, convertOther: convertOther);
+
+extension JArrayToDartList<E extends JObject?> on JArray<E> {
+  List<Object?> toDeepDartList({
+    Object? Function(JObject?) convertOther = _defaultDartConverter,
+  }) =>
+      map((e) => toDartObject(e, convertOther: convertOther)).toList();
+}
+
+extension JListToDartList<E extends JObject?> on JList<E> {
+  List<Object?> toDeepDartList({
+    Object? Function(JObject?) convertOther = _defaultDartConverter,
+  }) =>
+      map((e) => toDartObject(e, convertOther: convertOther)).toList();
+}
+
+extension JSetToDartSet<E extends JObject?> on JSet<E> {
+  Set<Object?> toDeepDartSet({
+    Object? Function(JObject?) convertOther = _defaultDartConverter,
+  }) =>
+      map((e) => toDartObject(e, convertOther: convertOther)).toSet();
+}
+
+extension JMapToDartMap<K extends JObject?, V extends JObject?> on JMap<K, V> {
+  Map<Object?, Object?> toDeepDartMap({
+    Object? Function(JObject?) convertOther = _defaultDartConverter,
+  }) =>
+      Map.fromEntries(
+        entries.map(
+          (e) => MapEntry(
+            toDartObject(e.key, convertOther: convertOther),
+            toDartObject(e.value, convertOther: convertOther),
+          ),
+        ),
+      );
+}
diff --git a/pkgs/jni/test/converter_test.dart b/pkgs/jni/test/converter_test.dart
new file mode 100644
index 0000000000..283c104abb
--- /dev/null
+++ b/pkgs/jni/test/converter_test.dart
@@ -0,0 +1,101 @@
+// Copyright (c) 2025, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:io';
+
+import 'package:jni/jni.dart';
+import 'package:test/test.dart';
+
+import 'test_util/test_util.dart';
+
+void main() {
+  if (!Platform.isAndroid) {
+    checkDylibIsUpToDate();
+    spawnJvm();
+  }
+  run(testRunner: test);
+}
+
+void run({required TestRunnerCallback testRunner}) {
+  testRunner('toJObject basic types', () {
+    using((arena) {
+      expect(toJObject(null), isNull);
+      expect(toJObject(true)!.isA(JBoolean.type), isTrue);
+      expect(toJObject(1)!.isA(JLong.type), isTrue);
+      expect(toJObject(1.5)!.isA(JDouble.type), isTrue);
+      expect(toJObject('abc')!.isA(JString.type), isTrue);
+    });
+  });
+
+  testRunner('toDartObject basic types', () {
+    using((arena) {
+      expect(toDartObject(null), isNull);
+      expect(toDartObject(true.toJBoolean()..releasedBy(arena)), true);
+      expect(toDartObject(1.toJLong()..releasedBy(arena)), 1);
+      expect(toDartObject(1.5.toJDouble()..releasedBy(arena)), 1.5);
+      expect(toDartObject('abc'.toJString()..releasedBy(arena)), 'abc');
+    });
+  });
+
+  testRunner('Deep conversion List', () {
+    using((arena) {
+      final list = [1, 'abc', true];
+      final jList = toJObject(list)!..releasedBy(arena);
+      expect(jList.isA(JList.type(JObject.nullableType)), isTrue);
+
+      final back = toDartObject(jList);
+      expect(back, isA<List>());
+      final backList = back as List;
+      expect(backList[0], 1);
+      expect(backList[1], 'abc');
+      expect(backList[2], true);
+    });
+  });
+
+  testRunner('Deep conversion Map', () {
+    using((arena) {
+      final map = {'a': 1, 'b': 2};
+      final jMap = toJObject(map)!..releasedBy(arena);
+      expect(jMap.isA(JMap.type(JObject.nullableType, JObject.nullableType)),
+          isTrue);
+
+      final back = toDartObject(jMap);
+      expect(back, isA<Map>());
+      final backMap = back as Map;
+      expect(backMap['a'], 1);
+      expect(backMap['b'], 2);
+    });
+  });
+
+  testRunner('Primitive arrays toJ*Array', () {
+    using((arena) {
+      final bools = [true, false].toJBooleanArray()..releasedBy(arena);
+      expect(bools.isA(JBooleanArray.type), isTrue);
+      expect(toDartObject(bools), [true, false]);
+
+      final ints = [1, 2, 3].toJIntArray()..releasedBy(arena);
+      expect(ints.isA(JIntArray.type), isTrue);
+      expect(toDartObject(ints), [1, 2, 3]);
+
+      final doubles = [1.5, 2.5].toJDoubleArray()..releasedBy(arena);
+      expect(doubles.isA(JDoubleArray.type), isTrue);
+      expect(toDartObject(doubles), [1.5, 2.5]);
+    });
+  });
+
+  testRunner('Object array toJObjectArray', () {
+    using((arena) {
+      final strings = [
+        'a'.toJString()..releasedBy(arena),
+        'b'.toJString()..releasedBy(arena)
+      ];
+      final jArray = strings.toJObjectArray(JString.type)..releasedBy(arena);
+      // Signature for JArray<JString> is [Ljava/lang/String;
+      expect(jArray.isA(JArray.type(JString.type)), isTrue);
+
+      final back = toDartObject(jArray);
+      expect(back, ['a', 'b']);
+    });
+  });
+}