He served as a first lieutenant in the United States Army for four years during World War II, commanding an infantry company.

He received four battle stars and a Purple Heart and took part in island campaigns at Kwajalein, Palau, Mindanao, and Okinawa.

Displeased with the way the governor was handling issues including the state's fiscal crisis as her re-election approached, Killian waged a bitter primary campaign against Grasso in 1978.

He lost and was replaced on the ticket by William A. O'Neill, who later succeeded Grasso as governor in 1980 after her resignation shortly before her death from cancer.

Killian was a Roman Catholic and a member of the American Bar Association (ABA), the Elks, the Knights of Columbus and the Friendly Sons of St. Patrick.