diff --git a/doc/source/whatsnew/v1.1.0.rst b/doc/source/whatsnew/v1.1.0.rst
index e07a8fa0469f4..cf2f507dc019c 100644
--- a/doc/source/whatsnew/v1.1.0.rst
+++ b/doc/source/whatsnew/v1.1.0.rst
@@ -150,6 +150,7 @@ Indexing
 - Bug in :meth:`PeriodIndex.get_loc` treating higher-resolution strings differently from :meth:`PeriodIndex.get_value` (:issue:`31172`)
 - Bug in :meth:`Series.at` and :meth:`DataFrame.at` not matching ``.loc`` behavior when looking up an integer in a :class:`Float64Index` (:issue:`31329`)
 - Bug in :meth:`PeriodIndex.is_monotonic` incorrectly returning ``True`` when containing leading ``NaT`` entries (:issue:`31437`)
+- Bug in :meth:`DatetimeIndex.get_loc` raising ``KeyError`` with converted-integer key instead of the user-passed key (:issue:`31425`)
 -
 
 Missing
diff --git a/pandas/core/indexes/base.py b/pandas/core/indexes/base.py
index 22ba317e78e63..9a56e0850aab0 100644
--- a/pandas/core/indexes/base.py
+++ b/pandas/core/indexes/base.py
@@ -2884,6 +2884,10 @@ def get_loc(self, key, method=None, tolerance=None):
                 return self._engine.get_loc(key)
             except KeyError:
                 return self._engine.get_loc(self._maybe_cast_indexer(key))
+
+        if tolerance is not None:
+            tolerance = self._convert_tolerance(tolerance, np.asarray(key))
+
         indexer = self.get_indexer([key], method=method, tolerance=tolerance)
         if indexer.ndim > 1 or indexer.size > 1:
             raise TypeError("get_loc requires scalar valued input")
diff --git a/pandas/core/indexes/datetimes.py b/pandas/core/indexes/datetimes.py
index 2b4636155111f..aea6d095e301e 100644
--- a/pandas/core/indexes/datetimes.py
+++ b/pandas/core/indexes/datetimes.py
@@ -639,18 +639,13 @@ def get_loc(self, key, method=None, tolerance=None):
         if not is_scalar(key):
             raise InvalidIndexError(key)
 
+        orig_key = key
         if is_valid_nat_for_dtype(key, self.dtype):
             key = NaT
 
-        if tolerance is not None:
-            # try converting tolerance now, so errors don't get swallowed by
-            # the try/except clauses below
-            tolerance = self._convert_tolerance(tolerance, np.asarray(key))
-
         if isinstance(key, (datetime, np.datetime64)):
             # needed to localize naive datetimes
             key = self._maybe_cast_for_get_loc(key)
-            return Index.get_loc(self, key, method, tolerance)
 
         elif isinstance(key, str):
             try:
@@ -659,9 +654,8 @@ def get_loc(self, key, method=None, tolerance=None):
                 pass
 
             try:
-                stamp = self._maybe_cast_for_get_loc(key)
-                return Index.get_loc(self, stamp, method, tolerance)
-            except (KeyError, ValueError):
+                key = self._maybe_cast_for_get_loc(key)
+            except ValueError:
                 raise KeyError(key)
 
         elif isinstance(key, timedelta):
@@ -670,14 +664,21 @@ def get_loc(self, key, method=None, tolerance=None):
                 f"Cannot index {type(self).__name__} with {type(key).__name__}"
             )
 
-        if isinstance(key, time):
+        elif isinstance(key, time):
             if method is not None:
                 raise NotImplementedError(
                     "cannot yet lookup inexact labels when key is a time object"
                 )
             return self.indexer_at_time(key)
 
-        return Index.get_loc(self, key, method, tolerance)
+        else:
+            # unrecognized type
+            raise KeyError(key)
+
+        try:
+            return Index.get_loc(self, key, method, tolerance)
+        except KeyError:
+            raise KeyError(orig_key)
 
     def _maybe_cast_for_get_loc(self, key) -> Timestamp:
         # needed to localize naive datetimes
diff --git a/pandas/core/indexes/timedeltas.py b/pandas/core/indexes/timedeltas.py
index 08a07e8d30348..5b5daee5557b2 100644
--- a/pandas/core/indexes/timedeltas.py
+++ b/pandas/core/indexes/timedeltas.py
@@ -1,7 +1,5 @@
 """ implement the TimedeltaIndex """
 
-import numpy as np
-
 from pandas._libs import NaT, Timedelta, index as libindex
 from pandas.util._decorators import Appender
 
@@ -262,11 +260,6 @@ def get_loc(self, key, method=None, tolerance=None):
         else:
             raise KeyError(key)
 
-        if tolerance is not None:
-            # try converting tolerance now, so errors don't get swallowed by
-            # the try/except clauses below
-            tolerance = self._convert_tolerance(tolerance, np.asarray(key))
-
         return Index.get_loc(self, key, method, tolerance)
 
     def _maybe_cast_slice_bound(self, label, side: str, kind):
diff --git a/pandas/tests/series/indexing/test_datetime.py b/pandas/tests/series/indexing/test_datetime.py
index 77085ef547690..813c195b36f67 100644
--- a/pandas/tests/series/indexing/test_datetime.py
+++ b/pandas/tests/series/indexing/test_datetime.py
@@ -1,4 +1,5 @@
 from datetime import datetime, timedelta
+import re
 
 import numpy as np
 import pytest
@@ -380,7 +381,7 @@ def test_datetime_indexing():
     s = Series(len(index), index=index)
     stamp = Timestamp("1/8/2000")
 
-    with pytest.raises(KeyError, match=r"^947289600000000000$"):
+    with pytest.raises(KeyError, match=re.escape(repr(stamp))):
         s[stamp]
     s[stamp] = 0
     assert s[stamp] == 0
@@ -389,7 +390,7 @@ def test_datetime_indexing():
     s = Series(len(index), index=index)
     s = s[::-1]
 
-    with pytest.raises(KeyError, match=r"^947289600000000000$"):
+    with pytest.raises(KeyError, match=re.escape(repr(stamp))):
         s[stamp]
     s[stamp] = 0
     assert s[stamp] == 0
@@ -495,8 +496,9 @@ def test_duplicate_dates_indexing(dups):
         expected = Series(np.where(mask, 0, ts), index=ts.index)
         tm.assert_series_equal(cp, expected)
 
-    with pytest.raises(KeyError, match=r"^947116800000000000$"):
-        ts[datetime(2000, 1, 6)]
+    key = datetime(2000, 1, 6)
+    with pytest.raises(KeyError, match=re.escape(repr(key))):
+        ts[key]
 
     # new index
     ts[datetime(2000, 1, 6)] = 0