Humphreys attended elementary and secondary school in Erie, Pennsylvania and then studied at Oberlin College (bachelor"s degree 1961) and from 1961 philosophy and mathematics at Cornell University. At Yale University he earned his master"s degree in 1964 and his Doctor of Philosophy in 1966 under George B. Seligman with thesis Algebraic Lie Algebras over fields of prime characteristic.
He is known as the author of several mathematical texts, especially Introduction to Lie Algebras and Representation Theory. In 1966 he became an assistant professor at the University of Oregon and in 1970 an associate professor at New York University. At the University of Massachusetts Amherst he became in 1974 an associate professor and in 1976 a full professor
In 2003 he retired there as professor emeritus.
In 1968/69 and in 1977 he was a visiting scholar at the Institute for Advanced Study and in 1969/70 at the Courant Institute of Mathematical Sciences of New York University. In 1985 he was a visiting professor at Rutgers University.
