Armstead spent his first two seasons as a backup to starter Jahad Thomas and rushed for 191 yards and two touchdowns as a freshman.

He received significantly more playing time as a sophomore and rushed for 919 yards on 156 carries and a team-leading 14 touchdowns as the Owls went on to win the American Athletic Conference (AAC) championship.

[3] Armstead finished his collegiate career as the Owls' fourth-leading rusher with 2,812 yards and fourth in school history with 34 rushing touchdowns.

[8] Armstead made his NFL debut in the Jaguars season opener on September 8, 2019, gaining seven yards on a single carry in a 40–26 loss to the Kansas City Chiefs.

On October 25, 2020, it was reported that he would miss the rest of the season due to COVID-19 and that he had been hospitalized twice having significant respiratory issues.

[19] On November 3, 2021, Armstead was signed to the Green Bay Packers practice squad.

[24] On June 30, 2023, Armstead signed with the Ottawa Redblacks of the Canadian Football League.