diff --git a/Userland/Libraries/LibWeb/HTML/MessageEvent.cpp b/Userland/Libraries/LibWeb/HTML/MessageEvent.cpp
index b877e111034..5b28be7570a 100644
--- a/Userland/Libraries/LibWeb/HTML/MessageEvent.cpp
+++ b/Userland/Libraries/LibWeb/HTML/MessageEvent.cpp
@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2022, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2024, Jamie Mansfield <jmansfield@cadixdev.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -75,4 +76,30 @@ JS::NonnullGCPtr<JS::Object> MessageEvent::ports() const
     return *m_ports_array;
 }
 
+// https://html.spec.whatwg.org/multipage/comms.html#dom-messageevent-initmessageevent
+void MessageEvent::init_message_event(String const& type, bool bubbles, bool cancelable, JS::Value data, String const& origin, String const& last_event_id, Optional<MessageEventSource> source, Vector<JS::Handle<MessagePort>> const& ports)
+{
+    // The initMessageEvent(type, bubbles, cancelable, data, origin, lastEventId, source, ports) method must initialize the event in a
+    // manner analogous to the similarly-named initEvent() method.
+
+    // 1. If this’s dispatch flag is set, then return.
+    if (dispatched())
+        return;
+
+    // 2. Initialize this with type, bubbles, and cancelable.
+    initialize_event(type, bubbles, cancelable);
+
+    // Implementation Defined: Initialise other values.
+    m_data = data;
+    m_origin = origin;
+    m_last_event_id = last_event_id;
+    m_source = source;
+    m_ports.clear();
+    m_ports.ensure_capacity(ports.size());
+    for (auto const& port : ports) {
+        VERIFY(port);
+        m_ports.unchecked_append(static_cast<JS::Object&>(*port));
+    }
+}
+
 }
diff --git a/Userland/Libraries/LibWeb/HTML/MessageEvent.h b/Userland/Libraries/LibWeb/HTML/MessageEvent.h
index 032ddbd2097..810c1b42774 100644
--- a/Userland/Libraries/LibWeb/HTML/MessageEvent.h
+++ b/Userland/Libraries/LibWeb/HTML/MessageEvent.h
@@ -40,6 +40,8 @@ public:
     JS::NonnullGCPtr<JS::Object> ports() const;
     Variant<JS::Handle<WindowProxy>, JS::Handle<MessagePort>, Empty> source() const;
 
+    void init_message_event(String const& type, bool bubbles, bool cancelable, JS::Value data, String const& origin, String const& last_event_id, Optional<MessageEventSource> source, Vector<JS::Handle<MessagePort>> const& ports);
+
 private:
     virtual void initialize(JS::Realm&) override;
     virtual void visit_edges(Cell::Visitor&) override;
diff --git a/Userland/Libraries/LibWeb/HTML/MessageEvent.idl b/Userland/Libraries/LibWeb/HTML/MessageEvent.idl
index ef13fc735c3..a85cb1e3eb1 100644
--- a/Userland/Libraries/LibWeb/HTML/MessageEvent.idl
+++ b/Userland/Libraries/LibWeb/HTML/MessageEvent.idl
@@ -15,6 +15,8 @@ interface MessageEvent : Event {
     readonly attribute MessageEventSource? source;
     // FIXME: readonly attribute FrozenArray<MessagePort> ports;
     readonly attribute any ports;
+
+    undefined initMessageEvent(DOMString type, optional boolean bubbles = false, optional boolean cancelable = false, optional any data = null, optional USVString origin = "", optional DOMString lastEventId = "", optional MessageEventSource? source = null, optional sequence<MessagePort> ports = []);
 };
 
 dictionary MessageEventInit : EventInit {