@@ -49,6 +49,11 @@ jobs:
           - os: macos-latest
             python-version: "pypy-3.10"
             deps: test
+          # Temporary CI run to use entry point compatible code in matplotlib-inline.
+          - os: ubuntu-latest
+            python-version: "3.12"
+            deps: test_extra
+            want-latest-entry-point-code: true
 
     steps:
     - uses: actions/checkout@v3
@@ -82,6 +87,16 @@ jobs:
     - name: Check manifest
       if: runner.os != 'Windows'  # setup.py does not support sdist on Windows
       run: check-manifest
+
+    - name: Install entry point compatible code (TEMPORARY)
+      if: matrix.want-latest-entry-point-code
+      run: |
+        python -m pip list
+        # Not installing matplotlib's entry point code as building matplotlib from source is complex.
+        # Rely upon matplotlib to test all the latest entry point branches together.
+        python -m pip install --upgrade git+https://github.com/ipython/matplotlib-inline.git@main
+        python -m pip list
+
     - name: pytest
       env:
         COLUMNS: 120
 
@@ -111,7 +111,7 @@ def display(
     display_id=None,
     raw=False,
     clear=False,
-    **kwargs
+    **kwargs,
 ):
     """Display a Python object in all frontends.
 
 
@@ -3657,7 +3657,7 @@ def enable_matplotlib(self, gui=None):
         from IPython.core import pylabtools as pt
         gui, backend = pt.find_gui_and_backend(gui, self.pylab_gui_select)
 
-        if gui != 'inline':
+        if gui != None:
             # If we have our first gui selection, store it
             if self.pylab_gui_select is None:
                 self.pylab_gui_select = gui
 
@@ -18,19 +18,19 @@
 from IPython.core.magic import Magics, magics_class, line_magic
 from IPython.testing.skipdoctest import skip_doctest
 from warnings import warn
-from IPython.core.pylabtools import backends
 
 #-----------------------------------------------------------------------------
 # Magic implementation classes
 #-----------------------------------------------------------------------------
 
 magic_gui_arg = magic_arguments.argument(
-        'gui', nargs='?',
-        help="""Name of the matplotlib backend to use %s.
+    "gui",
+    nargs="?",
+    help="""Name of the matplotlib backend to use such as 'qt' or 'widget'.
         If given, the corresponding matplotlib backend is used,
         otherwise it will be matplotlib's default
         (which you can set in your matplotlib config file).
-        """ % str(tuple(sorted(backends.keys())))
+        """,
 )
 
 
@@ -93,8 +93,12 @@ def matplotlib(self, line=''):
         """
         args = magic_arguments.parse_argstring(self.matplotlib, line)
         if args.list:
-            backends_list = list(backends.keys())
-            print("Available matplotlib backends: %s" % backends_list)
+            from IPython.core.pylabtools import _list_matplotlib_backends_and_gui_loops
+
+            print(
+                "Available matplotlib backends: %s"
+                % _list_matplotlib_backends_and_gui_loops()
+            )
         else:
             gui, backend = self.shell.enable_matplotlib(args.gui.lower() if isinstance(args.gui, str) else args.gui)
             self._show_matplotlib_backend(args.gui, backend)
 
@@ -12,9 +12,12 @@
 from IPython.core.display import _pngxy
 from IPython.utils.decorators import flag_calls
 
-# If user specifies a GUI, that dictates the backend, otherwise we read the
-# user's mpl default from the mpl rc structure
-backends = {
+
+# Matplotlib backend resolution functionality moved from IPython to Matplotlib
+# in IPython 8.24 and Matplotlib 3.9.1. Need to keep `backends` and `backend2gui`
+# here for earlier Matplotlib and for external backend libraries such as
+# mplcairo that might rely upon it.
+_deprecated_backends = {
     "tk": "TkAgg",
     "gtk": "GTKAgg",
     "gtk3": "GTK3Agg",
@@ -41,29 +44,44 @@
 # GUI support to activate based on the desired matplotlib backend.  For the
 # most part it's just a reverse of the above dict, but we also need to add a
 # few others that map to the same GUI manually:
-backend2gui = dict(zip(backends.values(), backends.keys()))
+_deprecated_backend2gui = dict(
+    zip(_deprecated_backends.values(), _deprecated_backends.keys())
+)
 # In the reverse mapping, there are a few extra valid matplotlib backends that
 # map to the same GUI support
-backend2gui["GTK"] = backend2gui["GTKCairo"] = "gtk"
-backend2gui["GTK3Cairo"] = "gtk3"
-backend2gui["GTK4Cairo"] = "gtk4"
-backend2gui["WX"] = "wx"
-backend2gui["CocoaAgg"] = "osx"
+_deprecated_backend2gui["GTK"] = _deprecated_backend2gui["GTKCairo"] = "gtk"
+_deprecated_backend2gui["GTK3Cairo"] = "gtk3"
+_deprecated_backend2gui["GTK4Cairo"] = "gtk4"
+_deprecated_backend2gui["WX"] = "wx"
+_deprecated_backend2gui["CocoaAgg"] = "osx"
 # There needs to be a hysteresis here as the new QtAgg Matplotlib backend
 # supports either Qt5 or Qt6 and the IPython qt event loop support Qt4, Qt5,
 # and Qt6.
-backend2gui["QtAgg"] = "qt"
-backend2gui["Qt4Agg"] = "qt4"
-backend2gui["Qt5Agg"] = "qt5"
+_deprecated_backend2gui["QtAgg"] = "qt"
+_deprecated_backend2gui["Qt4Agg"] = "qt4"
+_deprecated_backend2gui["Qt5Agg"] = "qt5"
 
 # And some backends that don't need GUI integration
-del backend2gui["nbAgg"]
-del backend2gui["agg"]
-del backend2gui["svg"]
-del backend2gui["pdf"]
-del backend2gui["ps"]
-del backend2gui["module://matplotlib_inline.backend_inline"]
-del backend2gui["module://ipympl.backend_nbagg"]
+del _deprecated_backend2gui["nbAgg"]
+del _deprecated_backend2gui["agg"]
+del _deprecated_backend2gui["svg"]
+del _deprecated_backend2gui["pdf"]
+del _deprecated_backend2gui["ps"]
+del _deprecated_backend2gui["module://matplotlib_inline.backend_inline"]
+del _deprecated_backend2gui["module://ipympl.backend_nbagg"]
+
+
+# Deprecated attributes backends and backend2gui mostly following PEP 562.
+def __getattr__(name):
+    if name in ("backends", "backend2gui"):
+        warnings.warn(
+            f"{name} is deprecated since IPython 8.24, backends are managed "
+            "in matplotlib and can be externally registered.",
+            DeprecationWarning,
+        )
+        return globals()[f"_deprecated_{name}"]
+    raise AttributeError(f"module {__name__!r} has no attribute {name!r}")
+
 
 #-----------------------------------------------------------------------------
 # Matplotlib utilities
@@ -267,7 +285,7 @@ def select_figure_formats(shell, formats, **kwargs):
 
     [ f.pop(Figure, None) for f in shell.display_formatter.formatters.values() ]
     mplbackend = matplotlib.get_backend().lower()
-    if mplbackend == 'nbagg' or mplbackend == 'module://ipympl.backend_nbagg':
+    if mplbackend in ("nbagg", "ipympl", "widget", "module://ipympl.backend_nbagg"):
         formatter = shell.display_formatter.ipython_display_formatter
         formatter.for_type(Figure, _reshow_nbagg_figure)
 
@@ -319,7 +337,23 @@ def find_gui_and_backend(gui=None, gui_select=None):
 
     import matplotlib
 
-    has_unified_qt_backend = getattr(matplotlib, "__version_info__", (0, 0)) >= (3, 5)
+    if _matplotlib_manages_backends():
+        backend_registry = matplotlib.backends.registry.backend_registry
+
+        # gui argument may be a gui event loop or may be a backend name.
+        if gui in ("auto", None):
+            backend = matplotlib.rcParamsOrig["backend"]
+            backend, gui = backend_registry.resolve_backend(backend)
+        else:
+            backend, gui = backend_registry.resolve_gui_or_backend(gui)
+
+        return gui, backend
+
+    # Fallback to previous behaviour (Matplotlib < 3.9)
+    mpl_version_info = getattr(matplotlib, "__version_info__", (0, 0))
+    has_unified_qt_backend = mpl_version_info >= (3, 5)
+
+    from IPython.core.pylabtools import backends
 
     backends_ = dict(backends)
     if not has_unified_qt_backend:
@@ -338,6 +372,7 @@ def find_gui_and_backend(gui=None, gui_select=None):
         backend = matplotlib.rcParamsOrig['backend']
         # In this case, we need to find what the appropriate gui selection call
         # should be for IPython, so we can activate inputhook accordingly
+        from IPython.core.pylabtools import backend2gui
         gui = backend2gui.get(backend, None)
 
         # If we have already had a gui active, we need it and inline are the
@@ -346,6 +381,11 @@ def find_gui_and_backend(gui=None, gui_select=None):
             gui = gui_select
             backend = backends_[gui]
 
+    # Matplotlib before _matplotlib_manages_backends() can return "inline" for
+    # no gui event loop rather than the None that IPython >= 8.24.0 expects.
+    if gui == "inline":
+        gui = None
+
     return gui, backend
 
 
@@ -431,3 +471,48 @@ def configure_inline_support(shell, backend):
     )
 
     configure_inline_support_orig(shell, backend)
+
+
+# Determine if Matplotlib manages backends only if needed, and cache result.
+# Do not read this directly, instead use _matplotlib_manages_backends().
+_matplotlib_manages_backends_value: bool | None = None
+
+
+def _matplotlib_manages_backends() -> bool:
+    """Return True if Matplotlib manages backends, False otherwise.
+
+    If it returns True, the caller can be sure that
+    matplotlib.backends.registry.backend_registry is available along with
+    member functions resolve_gui_or_backend, resolve_backend, list_all, and
+    list_gui_frameworks.
+    """
+    global _matplotlib_manages_backends_value
+    if _matplotlib_manages_backends_value is None:
+        try:
+            from matplotlib.backends.registry import backend_registry
+
+            _matplotlib_manages_backends_value = hasattr(
+                backend_registry, "resolve_gui_or_backend"
+            )
+        except ImportError:
+            _matplotlib_manages_backends_value = False
+
+    return _matplotlib_manages_backends_value
+
+
+def _list_matplotlib_backends_and_gui_loops() -> list[str]:
+    """Return list of all Matplotlib backends and GUI event loops.
+
+    This is the list returned by
+        %matplotlib --list
+    """
+    if _matplotlib_manages_backends():
+        from matplotlib.backends.registry import backend_registry
+
+        ret = backend_registry.list_all() + backend_registry.list_gui_frameworks()
+    else:
+        from IPython.core import pylabtools
+
+        ret = list(pylabtools.backends.keys())
+
+    return sorted(["auto"] + ret)