diff --git a/pandas/core/frame.py b/pandas/core/frame.py
index 0144aefedaa5f..5358fdb0b4dbd 100644
--- a/pandas/core/frame.py
+++ b/pandas/core/frame.py
@@ -4887,7 +4887,7 @@ def assign(self, **kwargs) -> DataFrame:
         Portland    17.0    62.6  290.15
         Berkeley    25.0    77.0  298.15
         """
-        data = self.copy()
+        data = self.copy(deep=None)
 
         for k, v in kwargs.items():
             data[k] = com.apply_if_callable(v, data)
diff --git a/pandas/tests/copy_view/test_methods.py b/pandas/tests/copy_view/test_methods.py
index bf65f153b10dd..6707f1411cbc7 100644
--- a/pandas/tests/copy_view/test_methods.py
+++ b/pandas/tests/copy_view/test_methods.py
@@ -280,3 +280,21 @@ def test_head_tail(method, using_copy_on_write):
         # without CoW enabled, head and tail return views. Mutating df2 also mutates df.
         df2.iloc[0, 0] = 1
     tm.assert_frame_equal(df, df_orig)
+
+
+def test_assign(using_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3]})
+    df_orig = df.copy()
+    df2 = df.assign()
+    df2._mgr._verify_integrity()
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+
+    # modify df2 to trigger CoW for that block
+    df2.iloc[0, 0] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    tm.assert_frame_equal(df, df_orig)