John McCullagh was born and raised in Brooklyn, New York, where he worked as a longshoreman on the Brooklyn waterfront, as a brewery truck driver, and also worked for the Juvenile Aid Bureau of the New York City Police Department. He attended Saint Bernard’s Seminary and College, Rochester, New York, and was ordained a Catholic priest on June 4, 1955. He served in Saint Athanasius Church in Brooklyn until January 1959, when he entered active duty as a U.S. Army chaplain. He earned his jump wings in August 1959, and over his career had 53 parachute jumps and participated in five airborne exercises in the United States. He was a graduate of the U.S. Army Chaplain Officer Advanced Course at Fort Hamilton, and also attended the Army Command and General Staff College at Fort Leavenworth, Kansas. He retired in 1979 as a U.S. Army colonel. He then served as a New York City police chaplain from 1981 until he retired in 2001. He was one of the Army’s top experts on drugs, and testified as an expert witness before the Senate Subcommittee on Alcohol and Narcotics.