Forel studied literature at the Sorbonne in Paris (1911-12) and medicine under César Roux at Lausanne (1912- 18).
Oscar-Louis Forel directed the psychiatric clinic La Métairie in Nyon from 1924 to 1929, then founded and directed the psychiatric clinic Les Rives de Prangins in Nyon (1929-46). From 1925 to 1953 he taught at the University of Geneva.
As a photographer, he made photos viewed extremely close up and framed to look like nonrepresentational painting. He calls his well-structured compositions "synchromies."
Forel was president of La Société Suisse de Psychiatric.