In 1990, he received his commission in the United States Army after graduating from Bloomsbury University.

[3] Morrissey commanded the 31st Air Defense Artillery Brigade from July 2012 to June 2014, when they deployed Operation Enduring Freedom.

He was then assigned as a legislative affairs staffer in the Office of the Secretary of Defense until June 2017 when he was reassigned as the United States Army Central director of operations.

[6] On February 26, 2020, he was assigned to the Missile Defense Agency as the director for test, where he oversaw testing of the RIM-161 Standard Missile 3, Terminal High Altitude Area Defense, and Aegis Combat System.

[1] In March 2022, Morrissey was reassigned as the director for plans and policy of the United States Space Command.