[1] He attended the New Mexico Military Institute prior to going to the United States Naval Academy, in which he graduated in 1944.

[2][3][4] From September 1969 to October 1971, following his promotion to rear admiral, Hannifin served as Commandant of the Thirteenth Naval District.

[3] He returned to Washington, D.C. in 1973 when he served in multiple positions within the Joint Chiefs of Staff.

In retirement Hannifin lived in Solana Beach, California and served as president of HANESCO, Co., in the oil and gas industry.

One son, Steven Patrick II also served in the United States Navy.