It is regularly found in Bolivia, Brazil, Peru, and Venezuela; as a vagrant in Argentina; and has possibly occurred in Ecuador.

[6] The South American Classification Committee of the American Ornithological Society (SACC), the International Ornithological Committee (IOC), and the Clements taxonomy assign these three subspecies to the sapphire-spangled emerald:[10][5][11] The HBW taxonomic system treats C. l. bartletti as a separate species, the spot-vented emerald (Amazilia bartletti).

[4] Males of subspecies C. l. zimmeri have a smaller patch of glittering violet-blue than the nominate; it does not extend from the throat onto the breast.

The nominate C. l. lactea is found in eastern Brazil from Bahia south through Minas Gerais, Rio de Janeiro, and São Paulo into Paraná.

C. l. bartletti is found in eastern and southeastern Peru, northern Bolivia, and adjacent western Brazil.

In addition to the semi-open landscapes, C. l. lactea is also found in open cerrado, campos rupestres, parks, and gardens.

[4] The eastern Brazilian sapphire-spangled emerald C. l. lactea makes short north-south seasonal movements that are apparently tied to the timing of its flowering nectar sources.

[4] The sapphire-spangled emerald forages for nectar at a wide variety of native and introduced flowering plants, shrubs, and trees.

Some favored families are Leguminaceae, Malvaceae, Heliconiaceae, Bromeliaceae, and Rubiaceae, with Verbenaceae and Lythraceae being lesser sources.

It builds a cup nest of plant down and spiderweb with lichen on the outside; it is typically placed as a "saddle" on a small branch.