diff --git a/doc/_static/mpl.css b/doc/_static/mpl.css
index 14a2b4732295..e9d7d65f3e01 100644
--- a/doc/_static/mpl.css
+++ b/doc/_static/mpl.css
@@ -9,6 +9,29 @@
     margin: 0;
 }
 
+/* Make announcement an error colour for unreleased documentation, and sticky. */
+#unreleased-message.bd-header-announcement {
+    border-bottom: solid var(--pst-color-danger-highlight);
+    color: var(--pst-color-danger-text);
+    font-weight: var(--pst-admonition-font-weight-heading);
+    position: sticky;
+    top: 0;
+    z-index: 1050;
+}
+
+#unreleased-message.bd-header-announcement:after {
+    background-color: var(--pst-color-danger);
+    opacity: 1;
+}
+
+#unreleased-message.bd-header-announcement a {
+    color: var(--pst-color-danger-text);
+}
+
+#unreleased-message.bd-header-announcement + .bd-navbar {
+    top: 3rem;  /* Minimum height of announcement header. */
+}
+
 /* multi column TOC */
 .contents ul {
     list-style-type: none;
diff --git a/doc/_templates/sections/announcement.html b/doc/_templates/sections/announcement.html
new file mode 100644
index 000000000000..b134acef9af5
--- /dev/null
+++ b/doc/_templates/sections/announcement.html
@@ -0,0 +1,13 @@
+{%- if theme_announcement == "unreleased" -%}
+{% set header_classes = ["bd-header-announcement", "container-fluid"] %}
+  <div class="{{ header_classes | join(' ') }}" id="unreleased-message">
+    <div class="bd-header-announcement__content">
+      You are reading documentation for the unreleased version of Matplotlib.
+      <a href="https://matplotlib.org/search.html?q={{ title | striptags | urlencode }}&amp;check_keywords=yes&amp;area=default">
+        Try searching for the released version of this page instead?
+      </a>
+    </div>
+  </div>
+{%- else -%}
+  {%- extends "!sections/announcement.html" -%}
+{%- endif %}
diff --git a/doc/conf.py b/doc/conf.py
index ce34993c3e8d..5375dba8f0ab 100644
--- a/doc/conf.py
+++ b/doc/conf.py
@@ -462,7 +462,11 @@ def js_tag_with_cache_busting(js):
     },
     "navbar_end": ["theme-switcher", "version-switcher", "mpl_icon_links"],
     "secondary_sidebar_items": "page-toc.html",
-     "footer_start": ["copyright", "sphinx-version", "doc_version"],
+    "footer_start": ["copyright", "sphinx-version", "doc_version"],
+    # We override the announcement template from pydata-sphinx-theme, where
+    # this special value indicates the use of the unreleased banner. If we need
+    # an actual announcement, then just place the text here as usual.
+    "announcement": "unreleased" if not is_release_build else "",
 }
 include_analytics = is_release_build
 if include_analytics: