diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8378fcf347..a650665c87 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -25,6 +25,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 - Fix `mpl_to_plotly` conversion of matplotlib contour lines and line collections: close contour rings ending with `Z` codes, support dash styles, convert date x-axes, separate disjoint subpaths with `None` separators, hide line collection traces from the legend by default, and group consecutive same-style lines into single traces [[#5770](https://github.com/plotly/plotly.py/pull/5770)], with thanks to @robertoffmoura for the contribution!
 - Fix `plotly.io.write_images` ignoring `layout.width`/`layout.height` (and the template's) and exporting every figure at the default 700x500 size; it now uses the same width/height priority as `write_image` and `to_image` [[#5784](https://github.com/plotly/plotly.py/pull/5784)], with thanks to @breken-ai for the contribution!
 - Fix color utilities mutating the list of colors passed to them [[#5836](https://github.com/plotly/plotly.py/pull/5836)], with thanks to @Enesuygurs for the contribution!
+- Fix timezone-aware `DatetimeIndex` values being converted to an object array, which made figure creation and `to_json()` much slower than for a timezone-aware Series; their JSON output now matches the Series output, without the UTC offset [[#5870](https://github.com/plotly/plotly.py/pull/5870)], with thanks to @somaz94 for the contribution!
 
 
 ## [7.1.0] - 2026-09-15
diff --git a/_plotly_utils/basevalidators.py b/_plotly_utils/basevalidators.py
index 1ffc63e5ad..6b26d0653e 100644
--- a/_plotly_utils/basevalidators.py
+++ b/_plotly_utils/basevalidators.py
@@ -105,6 +105,11 @@ def copy_to_readonly_numpy_array(v, kind=None, force_numeric=False):
         "O": "object",
     }
 
+    pd = get_module("pandas", should_load=False)
+    if pd is not None and isinstance(v, pd.Index):
+        # Narwhals passes an Index through unchanged, so use the Series path for it
+        v = v.to_series()
+
     # With `pass_through=True`, the original object will be returned if unable to convert
     # to a Narwhals DataFrame or Series.
     v = nw.from_native(v, allow_series=True, pass_through=True)
diff --git a/tests/test_plotly_utils/validators/test_pandas_series_input.py b/tests/test_plotly_utils/validators/test_pandas_series_input.py
index 04e41a722d..5706025117 100644
--- a/tests/test_plotly_utils/validators/test_pandas_series_input.py
+++ b/tests/test_plotly_utils/validators/test_pandas_series_input.py
@@ -186,6 +186,15 @@ def test_data_array_validator_dates_series(
     np.testing.assert_array_equal(res, dates_array)
 
 
+def test_data_array_validator_tz_aware_datetime_index(data_array_validator):
+    index = pd.date_range("2024-03-30", periods=3, freq="D", tz="Europe/Berlin")
+    res = data_array_validator.validate_coerce(index)
+
+    assert isinstance(res, np.ndarray)
+    assert res.dtype.kind == "M"
+    np.testing.assert_array_equal(res, index.tz_localize(None).to_numpy())
+
+
 def test_data_array_validator_dates_dataframe(
     data_array_validator, datetime_pandas, dates_array
 ):