He specialized in infectious diseases and was the author of more than 200 scientific papers.

Farmer was a recipient of numerous honors, including the 2020 Berggruen Prize for Philosophy and Culture, the Margaret Mead Award from the American Anthropological Association, the American Medical Association’s Outstanding International Physician (Nathan Davis) Award, a John D. and Catherine T. MacArthur Foundation Fellowship and, with his PIH colleagues, the Hilton Humanitarian Prize. He was a member of the National Academy of Medicine and of the American Academy of Arts and Sciences.