In 1935, Tompkins entered his psychiatric residency at the Veterans Administration (VA) Mental Hospital in Little Rock, Arkansas.
In 1945, as World War II ended, the VA medical service was reorganized and a Division of Psychiatry and Neurology was established.
He remained the director until 1955 when he resigned from the VA to accept a position at the St. Vincent's Catholic Medical Center in New York.
Tompkins served as a consultant during the planning and construction and upon completion; he headed the new psychiatric service until 1973 when he retired.
In 1965, he delivered the Maudsley Bequest Lecture at a joint meeting of the American Psychiatric Association and the Royal College of Psychiatrists.