At sea, Markham's Storm-Petrel favors the cool waters of the Humboldt current off Peru and northern Chile, but may be found between the latitutes of of 25°N and 30°S (Murphy 1936), and as far west as 118.02°W (Spear and Ainley 2007). In austral autumn (the nonbreeding season), highest densities have been documented just offshore from central Peru. In austral spring, some high density remains off southern Peru and northern Chile, but an even higher concentration congregates about 1700 km west of there as well (Spear and Ainley 2007).
The only known breeding site is on the Paracas Peninsula, in Ica, Peru (Jahncke 1993). There are surely other breeding localities, as much of the population still remains unaccounted for. Inland sightings and roadkill of adults and fledgelings around the Salar Grande, a large expanse of salt flats near Iquique, Chile (Brooke 2004), provides strong evidence for their presence in the Atacama desert of northern Chile and southern Peru.