diff --git a/doc/source/whatsnew/v2.2.0.rst b/doc/source/whatsnew/v2.2.0.rst
index 48aee18c90456..8127ce1fa6eda 100644
--- a/doc/source/whatsnew/v2.2.0.rst
+++ b/doc/source/whatsnew/v2.2.0.rst
@@ -473,6 +473,7 @@ Other
 - Bug in :func:`infer_freq` and :meth:`DatetimeIndex.inferred_freq` with weekly frequencies and non-nanosecond resolutions (:issue:`55609`)
 - Bug in :meth:`DataFrame.apply` where passing ``raw=True`` ignored ``args`` passed to the applied function (:issue:`55009`)
 - Bug in :meth:`Dataframe.from_dict` which would always sort the rows of the created :class:`DataFrame`.  (:issue:`55683`)
+- Bug in Cython :meth:`StringHashTable._unique` used ephemeral repr values when UnicodeEncodeError was raised (:issue:`45929`)
 - Bug in rendering ``inf`` values inside a a :class:`DataFrame` with the ``use_inf_as_na`` option enabled (:issue:`55483`)
 - Bug in rendering a :class:`Series` with a :class:`MultiIndex` when one of the index level's names is 0 not having that name displayed (:issue:`55415`)
 
diff --git a/pandas/_libs/hashtable_class_helper.pxi.in b/pandas/_libs/hashtable_class_helper.pxi.in
index 1cf5d734705af..79a0dfc6d723d 100644
--- a/pandas/_libs/hashtable_class_helper.pxi.in
+++ b/pandas/_libs/hashtable_class_helper.pxi.in
@@ -1128,6 +1128,7 @@ cdef class StringHashTable(HashTable):
         use_na_value = na_value is not None
 
         # assign pointers and pre-filter out missing (if ignore_na)
+        keep_rval_refs = []
         vecs = <const char **>malloc(n * sizeof(char *))
         for i in range(n):
             val = values[i]
@@ -1144,7 +1145,9 @@ cdef class StringHashTable(HashTable):
                 try:
                     v = get_c_string(<str>val)
                 except UnicodeEncodeError:
-                    v = get_c_string(<str>repr(val))
+                    rval = <str>repr(val)
+                    keep_rval_refs.append(rval)
+                    v = get_c_string(rval)
                 vecs[i] = v
 
         # compute
diff --git a/pandas/tests/base/test_unique.py b/pandas/tests/base/test_unique.py
index 4c845d8f24d01..fc9d6fedf20f0 100644
--- a/pandas/tests/base/test_unique.py
+++ b/pandas/tests/base/test_unique.py
@@ -97,7 +97,6 @@ def test_nunique_null(null_obj, index_or_series_obj):
         assert obj.nunique(dropna=False) == max(0, num_unique_values)
 
 
-@pytest.mark.single_cpu
 def test_unique_bad_unicode(index_or_series):
     # regression test for #34550
     uval = "\ud83d"  # smiley emoji
@@ -113,6 +112,24 @@ def test_unique_bad_unicode(index_or_series):
         tm.assert_numpy_array_equal(result, expected)
 
 
+def test_unique_45929(index_or_series):
+    # regression test for #45929
+    data_list = [
+        "1 \udcd6a NY",
+        "2 \udcd6b NY",
+        "3 \ud800c NY",
+        "4 \udcd6d NY",
+        "5 \udcc3e NY",
+    ]
+
+    obj = index_or_series(data_list)
+    assert len(obj.unique()) == len(data_list)
+    assert len(obj.value_counts()) == len(data_list)
+    assert len(np.unique(data_list)) == len(data_list)
+    assert len(set(data_list)) == len(data_list)
+    assert obj.is_unique
+
+
 @pytest.mark.parametrize("dropna", [True, False])
 def test_nunique_dropna(dropna):
     # GH37566