[1] He has deployed on missions to Bosnia, Croatia, Afghanistan and the Middle East, and served as Deputy Commanding General for Operations of the U.S. Army's I Corps at Joint Base Lewis-McChord, and as Commander of Joint Task Force Impact.

[2][3] He holds three master's degrees focused on war, defence and strategy has also served as Commander of the Canadian Army Doctrine and Training Centre since August 2020.

[1] St-Louis succeeded Major General Derek A. Macaulay as acting Commander of the Canadian Army on April 19, 2021.

[2] He assumed the position in an interim capacity while Lieutenant General Wayne Erye acts as Chief of the Defence Staff.

On July 13, 2022, St-Louis was appointed to serve as the Defence Attaché to the United States, succeeding Captain William Quinn.