Armstrong joined the college coaching ranks when he was hired as an assistant on Karen Hoppa's Auburn Tigers coaching staff in 2013.[2]
Armstrong was the head coach of the Mississippi State Bulldogs from 2019 to 2024, compiling an overall record of 62–35–18, which makes him the winningest coach in program history.[3] In his final season in Starkville, he led Mississippi State to go 10–0 in conference play to claim the first Southeastern Conference (SEC) regular-season title in program history, which led him to be named SEC Coach of the Year.[4]
Armstrong returned to Auburn in 2025, succeeding Hoppa after her retirement.[3]