BUG: Cannot use tz-aware origin in to_datetime (#16842)

doc/source/whatsnew/v0.21.0.txt

@@ -385,3 +385,4 @@ Other
 - Bug in :func:`eval` where the ``inplace`` parameter was being incorrectly handled (:issue:`16732`)
 - Bug in ``.isin()`` in which checking membership in empty ``Series`` objects raised an error (:issue:`16991`)
 - Bug in :func:`unique` where checking a tuple of strings raised a ``TypeError`` (:issue:`17108`)
+- Bug in :func:`to_datetime` that cannot use tz-aware origin (:issue:`16842`)

pandas/core/tools/datetimes.py

@@ -488,7 +488,11 @@ def _convert_listlike(arg, box, format, name=None, tz=tz):
 
         # we are going to offset back to unix / epoch time
         try:
-            offset = tslib.Timestamp(origin) - tslib.Timestamp(0)
+            origin_ts = tslib.Timestamp(origin)
+            epoch_ts = tslib.Timestamp(0)
+            if origin_ts.tzinfo is not None:
+                epoch_ts = epoch_ts.replace(tzinfo=origin_ts.tzinfo)
+            offset = origin_ts - epoch_ts
         except tslib.OutOfBoundsDatetime:
             raise tslib.OutOfBoundsDatetime(
                 "origin {} is Out of Bounds".format(origin))

pandas/tests/tseries/test_timezones.py

@@ -9,7 +9,7 @@
 from pytz import NonExistentTimeError
 from distutils.version import LooseVersion
 from dateutil.tz import tzlocal, tzoffset
-from datetime import datetime, timedelta, tzinfo, date
+from datetime import datetime, timedelta, tzinfo, date, timezone
 
 import pandas.util.testing as tm
 import pandas.core.tools.datetimes as tools
@@ -204,6 +204,13 @@ def test_timestamp_to_datetime_tzoffset(self):
         result = Timestamp(expected.to_pydatetime())
         assert expected == result
 
+    def test_timestamp_to_datetime_tzinfo(self):
+        # GH16842
+        expected = Timestamp('2000-01-02 00:00:00')
+        result = to_datetime(1, unit='D',
+                             origin=datetime(2000, 1, 1, tzinfo=timezone.utc))
+        assert expected == result
+
     def test_timedelta_push_over_dst_boundary(self):
         # #1389