[1] He was an Associate Director of the Hans Hofmann School and created, with Hoffman, two major mosaic murals in New York City.
The son of a labour union organiser,[2] he served in the United States Navy during the Second World War and then attended Goddard College, Plainfield, Vermont from 1947 to 1951 with American sculptor Richard Lippold, and fellow abstract artist Robert M. Fisher.
He then moved to New York City, and became involved in projects with abstract artist Hans Hofmann.
Gahagan's work was being exhibited in New York, Provincetown, San Francisco, Los Angeles and Paris.
The James Gahagan School of Fine Arts was opened from 1971–1974[1] in Woodbury, Vermont, and Gahagan was a guest teacher at Notre Dame University, Indiana, in 1978, Humboldt State University, California, in 1989, and the Vermont Studio Center from 1984 until 1999.