diff --git a/Libraries/LibJS/Runtime/StringPrototype.cpp b/Libraries/LibJS/Runtime/StringPrototype.cpp
index 6fe439fe0b32d4..8637f9afade673 100644
--- a/Libraries/LibJS/Runtime/StringPrototype.cpp
+++ b/Libraries/LibJS/Runtime/StringPrototype.cpp
@@ -81,6 +81,7 @@ StringPrototype::StringPrototype()
     put_native_function("substring", substring, 2, attr);
     put_native_function("includes", includes, 1, attr);
     put_native_function("slice", slice, 2, attr);
+    put_native_function("lastIndexOf", last_index_of, 1, attr);
 }
 
 StringPrototype::~StringPrototype()
@@ -425,4 +426,37 @@ Value StringPrototype::slice(Interpreter& interpreter)
     return js_string(interpreter, string_part);
 }
 
+Value StringPrototype::last_index_of(Interpreter& interpreter)
+{
+    auto string = string_from(interpreter);
+    if (string.is_null())
+        return {};
+
+    if (interpreter.argument_count() == 0)
+        return Value(-1);
+
+    auto search_string = interpreter.argument(0).to_string();
+    if (search_string.length() > string.length())
+        return Value(-1);
+
+    ssize_t max_index = string.length() - search_string.length();
+    ssize_t from_index = max_index;
+    if (interpreter.argument_count() >= 2) {
+        from_index = static_cast<ssize_t>(interpreter.argument(1).to_i32());
+
+        if (from_index < 0)
+            from_index = 0;
+        if (from_index > max_index)
+            from_index = max_index;
+    }
+
+    for (ssize_t i = from_index; i >= 0; --i) {
+        auto part_view = string.substring_view(i, search_string.length());
+        if (part_view == search_string)
+            return Value((i32)i);
+    }
+
+    return Value(-1);
+}
+
 }
diff --git a/Libraries/LibJS/Runtime/StringPrototype.h b/Libraries/LibJS/Runtime/StringPrototype.h
index df5221df7531f6..e25e6b648cb7b3 100644
--- a/Libraries/LibJS/Runtime/StringPrototype.h
+++ b/Libraries/LibJS/Runtime/StringPrototype.h
@@ -57,6 +57,7 @@ class StringPrototype final : public StringObject {
     static Value concat(Interpreter&);
     static Value includes(Interpreter&);
     static Value slice(Interpreter&);
+    static Value last_index_of(Interpreter&);
 };
 
 }
diff --git a/Libraries/LibJS/Tests/String.prototype.lastIndexOf.js b/Libraries/LibJS/Tests/String.prototype.lastIndexOf.js
new file mode 100644
index 00000000000000..dbd72147d7df1d
--- /dev/null
+++ b/Libraries/LibJS/Tests/String.prototype.lastIndexOf.js
@@ -0,0 +1,27 @@
+load("test-common.js");
+
+try {
+    assert(String.prototype.lastIndexOf.length === 1);
+    assert("hello friends".lastIndexOf() === -1);
+    assert("hello friends".lastIndexOf("e") === 9);
+    assert("hello friends".lastIndexOf("e", -7) === -1);
+    assert("hello friends".lastIndexOf("e", 100) === 9);
+    assert("hello friends".lastIndexOf("") === 13);
+    assert("hello friends".lastIndexOf("Z") === -1);
+    assert("hello friends".lastIndexOf("serenity") === -1);
+    assert("hello friends".lastIndexOf("", 4) === 4);
+    assert("hello serenity friends".lastIndexOf("serenity") === 6);
+    assert("hello serenity friends serenity".lastIndexOf("serenity") === 23);
+    assert("hello serenity friends serenity".lastIndexOf("serenity", 14) === 6);
+    assert("".lastIndexOf("") === 0);
+    assert("".lastIndexOf("", 1) === 0);
+    assert("".lastIndexOf("", -1) === 0);
+    assert("hello friends serenity".lastIndexOf("h", 10) === 0);
+    assert("hello friends serenity".lastIndexOf("l", 4) === 3);
+    assert("hello friends serenity".lastIndexOf("s", 13) === 12);
+    assert("hello".lastIndexOf("serenity") === -1);
+
+    console.log("PASS");
+} catch (err) {
+    console.log("FAIL: " + err);
+}