Raised in a blue-collar family in Rhode Island, Mullaney was the Bishop Hendricken High School valedictorian and was selected for nomination to the U.S. Military Academy in 1996. While a cadet, Mullaney double-majored in French and History, served as the cadet brigade operations officer in his senior year, and completed over 400 jumps as a nationally ranked member of West Point's sport-parachute team. He graduated second in the West Point Class of 2000.