Pablo Marcos was born in the small town of Laran, Chincha Alta, Peru,[2] and moved with his family to the capital, Lima, at age five.
Marcos later contributed caricatures to such weekly political magazines as Rochabus and Zamba Canuta while still an economics major at Peru's University of Lima.
[4] After another Creepy story and one in companion magazine Eerie that year, Marcos drew comics exclusively for rival Skywald Publications' Nightmare and Psycho from May 1972 to May 1973 cover-dates.
Marcos' color-comics interior-art debut came at publisher Martin Goodman's short-lived Atlas/Seaboard Comics, illustrating the sword-and-sorcery title Iron Jaw #3 (May 1975).
[4] His last known comics penciling for several years was the 14-page painted story "Om", scripted by Ron Fortier from a Marcos plot, in Quantum Cat Entertainment's Frank Frazetta Fantasy Illustrated #7 (July 1999).
He returned as an inker two years later on a handful of issues of CrossGen's Ruse, Mystic, Crux, and Silken Ghost through 2003, and once again did penciling from 2006 to 2008, on comics including Dynamite Entertainment's Red Sonja and Savage Tales.
[4] In the 1990s and 2000s, the Pablo Marcos Studio illustrated many books in Waldman Publishing's Great Illustrated Classics series of young-adult adaptations of such novels as Gulliver's Travels, The Wizard of Oz, The Invisible Man, The Legend of Sleepy Hollow and Rip Van Winkle,Jane Eyre,[6] The Jungle Book, King Solomon's Mines, A Little Princess, and The Three Musketeers.
Marcos reduced his workload in September 1985 in order to tend to his severely ill wife, a patient at New York University Medical Center, who died in November 1985.