He served as a U.S. Marine Corps Corporal, 1953–1955, was in private practice in Honolulu 1960-1986, and was director of the Legal Aid Society in Honolulu 1968-1971.
Kay was nominated by Ronald Reagan on July 3, 1986, to a new seat created by 98 Stat. 333 on the United States District Court for the District of Hawaii. He was confirmed by the United States Senate on September 12, 1986, and received his commission on September 15, 1986. Served as chief judge, 1991–1999 and assumed senior status on January 2, 2000.