diff --git i/lib/matplotlib/backends/backend_qt.py w/lib/matplotlib/backends/backend_qt.py
index c55937a019..1e0856adec 100644
--- i/lib/matplotlib/backends/backend_qt.py
+++ w/lib/matplotlib/backends/backend_qt.py
@@ -3,6 +3,7 @@ import operator
 import os
 import sys
 import traceback
+from weakref import WeakKeyDictionary
 
 import matplotlib as mpl
 from matplotlib import _api, backend_tools, cbook
@@ -646,7 +647,6 @@ class NavigationToolbar2QT(NavigationToolbar2, QtWidgets.QToolBar):
 
         self.coordinates = coordinates
         self._actions = {}  # mapping of toolitem method names to QActions.
-        self._subplot_dialog = None
 
         for text, tooltip_text, image_file, callback in self.toolitems:
             if text is None:
@@ -755,14 +755,11 @@ class NavigationToolbar2QT(NavigationToolbar2, QtWidgets.QToolBar):
         self.canvas.drawRectangle(None)
 
     def configure_subplots(self):
-        if self._subplot_dialog is None:
-            self._subplot_dialog = SubplotToolQt(
-                self.canvas.figure, self.canvas.parent())
-            self.canvas.mpl_connect(
-                "close_event", lambda e: self._subplot_dialog.reject())
-        self._subplot_dialog.update_from_current_subplotpars()
-        self._subplot_dialog.show()
-        return self._subplot_dialog
+        subplot_dialog = SubplotToolQt(
+            self.canvas.figure, self.canvas.parent())
+        subplot_dialog.update_from_current_subplotpars()
+        subplot_dialog.show()
+        return subplot_dialog
 
     def save_figure(self, *args):
         filetypes = self.canvas.get_supported_filetypes_grouped()
@@ -805,8 +802,13 @@ class NavigationToolbar2QT(NavigationToolbar2, QtWidgets.QToolBar):
 
 
 class SubplotToolQt(QtWidgets.QDialog):
-    def __init__(self, targetfig, parent):
-        super().__init__()
+    _keep_alive = WeakKeyDictionary()
+
+    def __new__(cls, targetfig, parent):
+        if targetfig in cls._keep_alive:
+            return cls._keep_alive[targetfig]
+        self = cls._keep_alive[targetfig] = super().__new__(cls, parent)
+        QtWidgets.QDialog.__init__(self)
         self.setWindowIcon(QtGui.QIcon(
             str(cbook._get_data_path("images/matplotlib.png"))))
         self.setObjectName("SubplotTool")
@@ -848,6 +850,11 @@ class SubplotToolQt(QtWidgets.QDialog):
         self._defaults = {}
         self._export_values_dialog = None
         self.update_from_current_subplotpars()
+        targetfig.canvas.mpl_connect("close_event", lambda e: self.reject())
+        return self
+
+    def __init__(self, targetfig, parent):
+        pass
 
     def update_from_current_subplotpars(self):
         self._defaults = {spinbox: getattr(self._figure.subplotpars, name)