He most recently served as the defensive line coach for the Ottawa Redblacks of the Canadian Football League (CFL).

He played professionally for the Baltimore Colts and the Ottawa Rough Riders for nine years where he was named the league's Most Outstanding Defensive Player in 1983.

On January 13, 2009, the Hamilton Tiger-Cats announced the hiring of Marshall as their new defensive co-ordinator and assistant head coach.

[1] On January 5, 2011, it was announced that Marshall had been hired by the Saskatchewan Roughriders to replace Ken Miller as head coach of the club.

In the following season, he led the team to a 4–4 record and a second consecutive playoff appearance, but the Varsity Blues lost again in the quarter-finals.