diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/ZonedDateTimePrototype.cpp b/Userland/Libraries/LibJS/Runtime/Temporal/ZonedDateTimePrototype.cpp
index da32e8ec8e..50c83ed960 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/ZonedDateTimePrototype.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/ZonedDateTimePrototype.cpp
@@ -72,6 +72,7 @@ void ZonedDateTimePrototype::initialize(GlobalObject& global_object)
     define_native_function(vm.names.equals, equals, 1, attr);
     define_native_function(vm.names.toString, to_string, 0, attr);
     define_native_function(vm.names.toLocaleString, to_locale_string, 0, attr);
+    define_native_function(vm.names.toJSON, to_json, 0, attr);
     define_native_function(vm.names.valueOf, value_of, 0, attr);
     define_native_function(vm.names.startOfDay, start_of_day, 0, attr);
     define_native_function(vm.names.toInstant, to_instant, 0, attr);
@@ -875,6 +876,17 @@ JS_DEFINE_NATIVE_FUNCTION(ZonedDateTimePrototype::to_locale_string)
     return js_string(vm, TRY(temporal_zoned_date_time_to_string(global_object, *zoned_date_time, "auto"sv, "auto"sv, "auto"sv, "auto"sv)));
 }
 
+// 6.3.43 Temporal.ZonedDateTime.prototype.toJSON ( ), https://tc39.es/proposal-temporal/#sec-temporal.zoneddatetime.prototype.tojson
+JS_DEFINE_NATIVE_FUNCTION(ZonedDateTimePrototype::to_json)
+{
+    // 1. Let zonedDateTime be the this value.
+    // 2. Perform ? RequireInternalSlot(zonedDateTime, [[InitializedTemporalZonedDateTime]]).
+    auto* zoned_date_time = TRY(typed_this_object(global_object));
+
+    // 3. Return ? TemporalZonedDateTimeToString(zonedDateTime, "auto", "auto", "auto", "auto").
+    return js_string(vm, TRY(temporal_zoned_date_time_to_string(global_object, *zoned_date_time, "auto"sv, "auto"sv, "auto"sv, "auto"sv)));
+}
+
 // 6.3.44 Temporal.ZonedDateTime.prototype.valueOf ( ), https://tc39.es/proposal-temporal/#sec-temporal.zoneddatetime.prototype.valueof
 JS_DEFINE_NATIVE_FUNCTION(ZonedDateTimePrototype::value_of)
 {
diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/ZonedDateTimePrototype.h b/Userland/Libraries/LibJS/Runtime/Temporal/ZonedDateTimePrototype.h
index 297423704f..c184db2213 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/ZonedDateTimePrototype.h
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/ZonedDateTimePrototype.h
@@ -56,6 +56,7 @@ private:
     JS_DECLARE_NATIVE_FUNCTION(equals);
     JS_DECLARE_NATIVE_FUNCTION(to_string);
     JS_DECLARE_NATIVE_FUNCTION(to_locale_string);
+    JS_DECLARE_NATIVE_FUNCTION(to_json);
     JS_DECLARE_NATIVE_FUNCTION(value_of);
     JS_DECLARE_NATIVE_FUNCTION(start_of_day);
     JS_DECLARE_NATIVE_FUNCTION(to_instant);
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Temporal/ZonedDateTime/ZonedDateTime.prototype.toJSON.js b/Userland/Libraries/LibJS/Tests/builtins/Temporal/ZonedDateTime/ZonedDateTime.prototype.toJSON.js
new file mode 100644
index 0000000000..844038b815
--- /dev/null
+++ b/Userland/Libraries/LibJS/Tests/builtins/Temporal/ZonedDateTime/ZonedDateTime.prototype.toJSON.js
@@ -0,0 +1,20 @@
+describe("correct behavior", () => {
+    test("length is 0", () => {
+        expect(Temporal.ZonedDateTime.prototype.toJSON).toHaveLength(0);
+    });
+
+    test("basic functionality", () => {
+        const plainDateTime = new Temporal.PlainDateTime(2021, 11, 3, 1, 33, 5, 100, 200, 300);
+        const timeZone = new Temporal.TimeZone("UTC");
+        const zonedDateTime = plainDateTime.toZonedDateTime(timeZone);
+        expect(zonedDateTime.toJSON()).toBe("2021-11-03T01:33:05.1002003+00:00[UTC]");
+    });
+});
+
+describe("errors", () => {
+    test("this value must be a Temporal.ZonedDateTime object", () => {
+        expect(() => {
+            Temporal.ZonedDateTime.prototype.toJSON.call("foo");
+        }).toThrowWithMessage(TypeError, "Not an object of type Temporal.ZonedDateTime");
+    });
+});