diff --git a/Libraries/LibWeb/HTML/HTMLElement.cpp b/Libraries/LibWeb/HTML/HTMLElement.cpp
index 9800437210c..a172759bbfe 100644
--- a/Libraries/LibWeb/HTML/HTMLElement.cpp
+++ b/Libraries/LibWeb/HTML/HTMLElement.cpp
@@ -153,10 +153,55 @@ void HTMLElement::set_inner_text(StringView text)
     set_needs_style_update(true);
 }
 
-// https://html.spec.whatwg.org/multipage/dom.html#the-innertext-idl-attribute:dom-outertext-2
-WebIDL::ExceptionOr<void> HTMLElement::set_outer_text(String)
+// https://html.spec.whatwg.org/multipage/dom.html#merge-with-the-next-text-node
+static void merge_with_the_next_text_node(DOM::Text& node)
 {
-    dbgln("FIXME: Implement HTMLElement::set_outer_text()");
+    // 1. Let next be node's next sibling.
+    auto next = node.next_sibling();
+
+    // 2. If next is not a Text node, then return.
+    if (!is<DOM::Text>(next))
+        return;
+
+    // 3. Replace data with node, node's data's length, 0, and next's data.
+    MUST(node.replace_data(node.length_in_utf16_code_units(), 0, static_cast<DOM::Text const&>(*next).data()));
+
+    // 4. Remove next.
+    next->remove();
+}
+
+// https://html.spec.whatwg.org/multipage/dom.html#the-innertext-idl-attribute:dom-outertext-2
+WebIDL::ExceptionOr<void> HTMLElement::set_outer_text(String const& value)
+{
+    // 1. If this's parent is null, then throw a "NoModificationAllowedError" DOMException.
+    if (!parent())
+        return WebIDL::NoModificationAllowedError::create(realm(), "setOuterText: parent is null"_string);
+
+    // 2. Let next be this's next sibling.
+    auto* next = next_sibling();
+
+    // 3. Let previous be this's previous sibling.
+    auto* previous = previous_sibling();
+
+    // 4. Let fragment be the rendered text fragment for the given value given this's node document.
+    auto fragment = rendered_text_fragment(value);
+
+    // 5. If fragment has no children, then append a new Text node whose data is the empty string and node document is this's node document to fragment.
+    if (!fragment->has_children())
+        MUST(fragment->append_child(document().create_text_node(String {})));
+
+    // 6. Replace this with fragment within this's parent.
+    MUST(parent()->replace_child(fragment, *this));
+
+    // 7. If next is non-null and next's previous sibling is a Text node, then merge with the next text node given next's previous sibling.
+    if (next && is<DOM::Text>(next->previous_sibling()))
+        merge_with_the_next_text_node(static_cast<DOM::Text&>(*next->previous_sibling()));
+
+    // 8. If previous is a Text node, then merge with the next text node given previous.
+    if (is<DOM::Text>(previous))
+        merge_with_the_next_text_node(static_cast<DOM::Text&>(*previous));
+
+    set_needs_style_update(true);
     return {};
 }
 
diff --git a/Libraries/LibWeb/HTML/HTMLElement.h b/Libraries/LibWeb/HTML/HTMLElement.h
index feb47862570..6e29a48b105 100644
--- a/Libraries/LibWeb/HTML/HTMLElement.h
+++ b/Libraries/LibWeb/HTML/HTMLElement.h
@@ -45,7 +45,7 @@ public:
     void set_inner_text(StringView);
 
     [[nodiscard]] String outer_text();
-    WebIDL::ExceptionOr<void> set_outer_text(String);
+    WebIDL::ExceptionOr<void> set_outer_text(String const&);
 
     int offset_top() const;
     int offset_left() const;
diff --git a/Tests/LibWeb/Text/expected/wpt-import/html/dom/elements/the-innertext-and-outertext-properties/outertext-setter.txt b/Tests/LibWeb/Text/expected/wpt-import/html/dom/elements/the-innertext-and-outertext-properties/outertext-setter.txt
index 8b63fe2ff8a..ced1f9f078b 100644
--- a/Tests/LibWeb/Text/expected/wpt-import/html/dom/elements/the-innertext-and-outertext-properties/outertext-setter.txt
+++ b/Tests/LibWeb/Text/expected/wpt-import/html/dom/elements/the-innertext-and-outertext-properties/outertext-setter.txt
@@ -6,49 +6,48 @@ Rerun
 
 Found 43 tests
 
-2 Pass
-41 Fail
+43 Pass
 Details
-Result	Test Name	MessageFail	Replacing a node and merging with the previous text node	
-Fail	Replacing a node and merging with the following text node	
-Fail	Replacing a node and merging with the previous and following text node	
-Fail	Only merges with the previous and following text nodes, does not completely normalize	
-Fail	Empty string	
-Fail	Empty string with surrounding text nodes	
-Fail	Setting outerText to a bunch of newlines creates a bunch of <br>s with no text nodes	
-Fail	Removing a node	
-Fail	Detached node	
-Fail	Simplest possible test	
-Fail	Newlines convert to <br> in non-white-space:pre elements	
-Fail	Newlines convert to <br> in <pre> element	
-Fail	Newlines convert to <br> in <textarea> element	
-Fail	Newlines convert to <br> in white-space:pre element	
-Fail	CRs convert to <br> in non-white-space:pre elements	
-Fail	CRs convert to <br> in <pre> element	
-Fail	Newline/CR pair converts to <br> in non-white-space:pre element	
-Fail	Newline/newline pair converts to two <br>s in non-white-space:pre element	
-Fail	CR/CR pair converts to two <br>s in non-white-space:pre element	
-Fail	CRs convert to <br> in white-space:pre element	
-Fail	< preserved	
-Fail	> preserved	
-Fail	& preserved	
-Fail	" preserved	
-Fail	' preserved	
+Result	Test Name	MessagePass	Replacing a node and merging with the previous text node	
+Pass	Replacing a node and merging with the following text node	
+Pass	Replacing a node and merging with the previous and following text node	
+Pass	Only merges with the previous and following text nodes, does not completely normalize	
+Pass	Empty string	
+Pass	Empty string with surrounding text nodes	
+Pass	Setting outerText to a bunch of newlines creates a bunch of <br>s with no text nodes	
+Pass	Removing a node	
+Pass	Detached node	
+Pass	Simplest possible test	
+Pass	Newlines convert to <br> in non-white-space:pre elements	
+Pass	Newlines convert to <br> in <pre> element	
+Pass	Newlines convert to <br> in <textarea> element	
+Pass	Newlines convert to <br> in white-space:pre element	
+Pass	CRs convert to <br> in non-white-space:pre elements	
+Pass	CRs convert to <br> in <pre> element	
+Pass	Newline/CR pair converts to <br> in non-white-space:pre element	
+Pass	Newline/newline pair converts to two <br>s in non-white-space:pre element	
+Pass	CR/CR pair converts to two <br>s in non-white-space:pre element	
+Pass	CRs convert to <br> in white-space:pre element	
+Pass	< preserved	
+Pass	> preserved	
+Pass	& preserved	
+Pass	" preserved	
+Pass	' preserved	
 Pass	outerText not supported on SVG elements	
 Pass	outerText not supported on MathML elements	
-Fail	Null characters preserved	
-Fail	Tabs preserved	
-Fail	Leading whitespace preserved	
-Fail	Trailing whitespace preserved	
-Fail	Whitespace not compressed	
-Fail	Existing text deleted	
-Fail	Existing <br> deleted	
-Fail	Assigning the empty string	
-Fail	Assigning null	
-Fail	Assigning undefined	
-Fail	Start with CR	
-Fail	Start with LF	
-Fail	Start with CRLF	
-Fail	End with CR	
-Fail	End with LF	
-Fail	End with CRLF	
\ No newline at end of file
+Pass	Null characters preserved	
+Pass	Tabs preserved	
+Pass	Leading whitespace preserved	
+Pass	Trailing whitespace preserved	
+Pass	Whitespace not compressed	
+Pass	Existing text deleted	
+Pass	Existing <br> deleted	
+Pass	Assigning the empty string	
+Pass	Assigning null	
+Pass	Assigning undefined	
+Pass	Start with CR	
+Pass	Start with LF	
+Pass	Start with CRLF	
+Pass	End with CR	
+Pass	End with LF	
+Pass	End with CRLF	
\ No newline at end of file