Xantus's hummingbird is found from central Baja California south to the peninsula's tip. It has also been recorded as a vagrant twice in California and once in British Columbia. The species inhabits arid woodlands of scrub, oak, and pine-oak at elevations between 490 and 4,900 ft and also visits coastal desert, gardens, and feeders.

Xantus's hummingbird breeds between July and September or October in the northern part of its range and February to April in the south with a gradient between the areas. The nest is a cup of fine plant fibers, other plant materials, and small feathers bound with spiderweb and decorated with lichen and bark. It is usually suspended from the end of a thin branch within about 3 to 7 ft above the ground or often above water. The female incubates the clutch of two eggs for 15 to 16 days and fledging occurs about 22 days after hatch.