diff --git a/Libraries/LibJS/Runtime/Temporal/PlainDatePrototype.cpp b/Libraries/LibJS/Runtime/Temporal/PlainDatePrototype.cpp
index 0cc023c8f10..5f18f999565 100644
--- a/Libraries/LibJS/Runtime/Temporal/PlainDatePrototype.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/PlainDatePrototype.cpp
@@ -10,7 +10,9 @@
 #include <LibJS/Runtime/Temporal/Calendar.h>
 #include <LibJS/Runtime/Temporal/Duration.h>
 #include <LibJS/Runtime/Temporal/PlainDatePrototype.h>
+#include <LibJS/Runtime/Temporal/PlainDateTime.h>
 #include <LibJS/Runtime/Temporal/PlainMonthDay.h>
+#include <LibJS/Runtime/Temporal/PlainTime.h>
 #include <LibJS/Runtime/Temporal/PlainYearMonth.h>
 
 namespace JS::Temporal {
@@ -59,6 +61,7 @@ void PlainDatePrototype::initialize(Realm& realm)
     define_native_function(realm, vm.names.until, until, 1, attr);
     define_native_function(realm, vm.names.since, since, 1, attr);
     define_native_function(realm, vm.names.equals, equals, 1, attr);
+    define_native_function(realm, vm.names.toPlainDateTime, to_plain_date_time, 0, attr);
     define_native_function(realm, vm.names.toString, to_string, 0, attr);
     define_native_function(realm, vm.names.toLocaleString, to_locale_string, 0, attr);
     define_native_function(realm, vm.names.toJSON, to_json, 0, attr);
@@ -362,6 +365,25 @@ JS_DEFINE_NATIVE_FUNCTION(PlainDatePrototype::equals)
     return calendar_equals(temporal_date->calendar(), other->calendar());
 }
 
+// 3.3.28 Temporal.PlainDate.prototype.toPlainDateTime ( [ temporalTime ] ), https://tc39.es/proposal-temporal/#sec-temporal.plaindate.prototype.toplaindatetime
+JS_DEFINE_NATIVE_FUNCTION(PlainDatePrototype::to_plain_date_time)
+{
+    auto temporal_time = vm.argument(0);
+
+    // 1. Let temporalDate be the this value.
+    // 2. Perform ? RequireInternalSlot(temporalDate, [[InitializedTemporalDate]]).
+    auto temporal_date = TRY(typed_this_object(vm));
+
+    // 3. Let time be ? ToTimeRecordOrMidnight(temporalTime).
+    auto time = TRY(to_time_record_or_midnight(vm, temporal_time));
+
+    // 4. Let isoDateTime be CombineISODateAndTimeRecord(temporalDate.[[ISODate]], time).
+    auto iso_date_time = combine_iso_date_and_time_record(temporal_date->iso_date(), time);
+
+    // 5. Return ? CreateTemporalDateTime(isoDateTime, temporalDate.[[Calendar]]).
+    return TRY(create_temporal_date_time(vm, iso_date_time, temporal_date->calendar()));
+}
+
 // 3.3.30 Temporal.PlainDate.prototype.toString ( [ options ] ), https://tc39.es/proposal-temporal/#sec-temporal.plaindate.prototype.tostring
 JS_DEFINE_NATIVE_FUNCTION(PlainDatePrototype::to_string)
 {
diff --git a/Libraries/LibJS/Runtime/Temporal/PlainDatePrototype.h b/Libraries/LibJS/Runtime/Temporal/PlainDatePrototype.h
index 1a02652a1b2..d9bbbb94bc8 100644
--- a/Libraries/LibJS/Runtime/Temporal/PlainDatePrototype.h
+++ b/Libraries/LibJS/Runtime/Temporal/PlainDatePrototype.h
@@ -48,6 +48,7 @@ private:
     JS_DECLARE_NATIVE_FUNCTION(until);
     JS_DECLARE_NATIVE_FUNCTION(since);
     JS_DECLARE_NATIVE_FUNCTION(equals);
+    JS_DECLARE_NATIVE_FUNCTION(to_plain_date_time);
     JS_DECLARE_NATIVE_FUNCTION(to_string);
     JS_DECLARE_NATIVE_FUNCTION(to_locale_string);
     JS_DECLARE_NATIVE_FUNCTION(to_json);
diff --git a/Libraries/LibJS/Tests/builtins/Temporal/PlainDate/PlainDate.prototype.toPlainDateTime.js b/Libraries/LibJS/Tests/builtins/Temporal/PlainDate/PlainDate.prototype.toPlainDateTime.js
new file mode 100644
index 00000000000..69fdb1cc48b
--- /dev/null
+++ b/Libraries/LibJS/Tests/builtins/Temporal/PlainDate/PlainDate.prototype.toPlainDateTime.js
@@ -0,0 +1,20 @@
+describe("correct behavior", () => {
+    test("length is 0", () => {
+        expect(Temporal.PlainDate.prototype.toPlainDateTime).toHaveLength(0);
+    });
+
+    test("basic functionality", () => {
+        const plainDate = new Temporal.PlainDate(2021, 8, 27);
+        const plainTime = new Temporal.PlainTime(18, 11, 44, 1, 2, 3);
+        const plainDateTime = plainDate.toPlainDateTime(plainTime);
+        expect(plainDateTime.year).toBe(2021);
+        expect(plainDateTime.month).toBe(8);
+        expect(plainDateTime.day).toBe(27);
+        expect(plainDateTime.hour).toBe(18);
+        expect(plainDateTime.minute).toBe(11);
+        expect(plainDateTime.second).toBe(44);
+        expect(plainDateTime.millisecond).toBe(1);
+        expect(plainDateTime.microsecond).toBe(2);
+        expect(plainDateTime.nanosecond).toBe(3);
+    });
+});