diff --git a/Userland/Libraries/LibWeb/CMakeLists.txt b/Userland/Libraries/LibWeb/CMakeLists.txt
index dca6a1c41fd..da046c9cc45 100644
--- a/Userland/Libraries/LibWeb/CMakeLists.txt
+++ b/Userland/Libraries/LibWeb/CMakeLists.txt
@@ -411,6 +411,7 @@ set(SOURCES
     HTML/NavigationDestination.cpp
     HTML/NavigationCurrentEntryChangeEvent.cpp
     HTML/NavigationHistoryEntry.cpp
+    HTML/NavigationObserver.cpp
     HTML/NavigationParams.cpp
     HTML/NavigationTransition.cpp
     HTML/Navigator.cpp
diff --git a/Userland/Libraries/LibWeb/Forward.h b/Userland/Libraries/LibWeb/Forward.h
index 6392ad692c3..aba1ae04b07 100644
--- a/Userland/Libraries/LibWeb/Forward.h
+++ b/Userland/Libraries/LibWeb/Forward.h
@@ -496,6 +496,7 @@ class Navigation;
 class NavigationCurrentEntryChangeEvent;
 class NavigationDestination;
 class NavigationHistoryEntry;
+class NavigationObserver;
 class NavigationTransition;
 class Navigator;
 class PageTransitionEvent;
diff --git a/Userland/Libraries/LibWeb/HTML/Navigable.cpp b/Userland/Libraries/LibWeb/HTML/Navigable.cpp
index 9dcf7b4aa8f..56e3bd3b090 100644
--- a/Userland/Libraries/LibWeb/HTML/Navigable.cpp
+++ b/Userland/Libraries/LibWeb/HTML/Navigable.cpp
@@ -23,6 +23,7 @@
 #include <LibWeb/HTML/HistoryHandlingBehavior.h>
 #include <LibWeb/HTML/Navigable.h>
 #include <LibWeb/HTML/Navigation.h>
+#include <LibWeb/HTML/NavigationObserver.h>
 #include <LibWeb/HTML/NavigationParams.h>
 #include <LibWeb/HTML/POSTResource.h>
 #include <LibWeb/HTML/Parser/HTMLParser.h>
@@ -126,6 +127,7 @@ void Navigable::visit_edges(Cell::Visitor& visitor)
     visitor.visit(m_current_session_history_entry);
     visitor.visit(m_active_session_history_entry);
     visitor.visit(m_container);
+    visitor.visit(m_navigation_observers);
     m_event_handler.visit_edges(visitor);
 }
 
@@ -230,6 +232,13 @@ void Navigable::activate_history_entry(JS::GCPtr<SessionHistoryEntry> entry)
 
     // 5. Make active newDocument.
     new_document->make_active();
+
+    if (m_ongoing_navigation.has<Empty>()) {
+        for (auto navigation_observer : m_navigation_observers) {
+            if (navigation_observer->navigation_complete())
+                navigation_observer->navigation_complete()->function()();
+        }
+    }
 }
 
 // https://html.spec.whatwg.org/multipage/document-sequences.html#nav-document
@@ -2200,4 +2209,16 @@ void Navigable::paste(String const& text)
     m_event_handler.handle_paste(text);
 }
 
+void Navigable::register_navigation_observer(Badge<NavigationObserver>, NavigationObserver& navigation_observer)
+{
+    auto result = m_navigation_observers.set(navigation_observer);
+    VERIFY(result == AK::HashSetResult::InsertedNewEntry);
+}
+
+void Navigable::unregister_navigation_observer(Badge<NavigationObserver>, NavigationObserver& navigation_observer)
+{
+    bool was_removed = m_navigation_observers.remove(navigation_observer);
+    VERIFY(was_removed);
+}
+
 }
diff --git a/Userland/Libraries/LibWeb/HTML/Navigable.h b/Userland/Libraries/LibWeb/HTML/Navigable.h
index 8283dff578d..5d65b99ea9e 100644
--- a/Userland/Libraries/LibWeb/HTML/Navigable.h
+++ b/Userland/Libraries/LibWeb/HTML/Navigable.h
@@ -59,6 +59,9 @@ public:
 
     ErrorOr<void> initialize_navigable(JS::NonnullGCPtr<DocumentState> document_state, JS::GCPtr<Navigable> parent);
 
+    void register_navigation_observer(Badge<NavigationObserver>, NavigationObserver&);
+    void unregister_navigation_observer(Badge<NavigationObserver>, NavigationObserver&);
+
     Vector<JS::Handle<Navigable>> child_navigables() const;
 
     bool is_traversable() const;
@@ -232,6 +235,8 @@ private:
 
     JS::NonnullGCPtr<Page> m_page;
 
+    HashTable<JS::NonnullGCPtr<NavigationObserver>> m_navigation_observers;
+
     bool m_has_been_destroyed { false };
 
     CSSPixelSize m_size;
diff --git a/Userland/Libraries/LibWeb/HTML/NavigationObserver.cpp b/Userland/Libraries/LibWeb/HTML/NavigationObserver.cpp
new file mode 100644
index 00000000000..7b95ccfa0e7
--- /dev/null
+++ b/Userland/Libraries/LibWeb/HTML/NavigationObserver.cpp
@@ -0,0 +1,43 @@
+/*
+ * Copyright (c) 2024, Tim Flynn <trflynn89@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibJS/Runtime/Realm.h>
+#include <LibWeb/HTML/Navigable.h>
+#include <LibWeb/HTML/NavigationObserver.h>
+
+namespace Web::HTML {
+
+JS_DEFINE_ALLOCATOR(NavigationObserver);
+
+NavigationObserver::NavigationObserver(JS::Realm& realm, Navigable& navigable)
+    : Bindings::PlatformObject(realm)
+    , m_navigable(navigable)
+{
+    m_navigable->register_navigation_observer({}, *this);
+}
+
+void NavigationObserver::visit_edges(Cell::Visitor& visitor)
+{
+    Base::visit_edges(visitor);
+    visitor.visit(m_navigable);
+    visitor.visit(m_navigation_complete);
+}
+
+void NavigationObserver::finalize()
+{
+    Base::finalize();
+    m_navigable->unregister_navigation_observer({}, *this);
+}
+
+void NavigationObserver::set_navigation_complete(Function<void()> callback)
+{
+    if (callback)
+        m_navigation_complete = JS::create_heap_function(vm().heap(), move(callback));
+    else
+        m_navigation_complete = nullptr;
+}
+
+}
diff --git a/Userland/Libraries/LibWeb/HTML/NavigationObserver.h b/Userland/Libraries/LibWeb/HTML/NavigationObserver.h
new file mode 100644
index 00000000000..03be96d23b9
--- /dev/null
+++ b/Userland/Libraries/LibWeb/HTML/NavigationObserver.h
@@ -0,0 +1,34 @@
+/*
+ * Copyright (c) 2024, Tim Flynn <trflynn89@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibJS/Heap/GCPtr.h>
+#include <LibJS/Heap/HeapFunction.h>
+#include <LibWeb/Bindings/PlatformObject.h>
+#include <LibWeb/Forward.h>
+
+namespace Web::HTML {
+
+class NavigationObserver final : public Bindings::PlatformObject {
+    WEB_PLATFORM_OBJECT(NavigationObserver, Bindings::PlatformObject);
+    JS_DECLARE_ALLOCATOR(NavigationObserver);
+
+public:
+    [[nodiscard]] JS::GCPtr<JS::HeapFunction<void()>> navigation_complete() const { return m_navigation_complete; }
+    void set_navigation_complete(Function<void()>);
+
+private:
+    NavigationObserver(JS::Realm&, Navigable&);
+
+    virtual void visit_edges(Cell::Visitor&) override;
+    virtual void finalize() override;
+
+    JS::NonnullGCPtr<Navigable> m_navigable;
+    JS::GCPtr<JS::HeapFunction<void()>> m_navigation_complete;
+};
+
+}