After his playing career ended, Marshall ventured into coaching semi-professional football. In 1990, Marshall served as head coach for the Ottawa Bootleggers of the
Empire Football League. The next three years, he served as head coach for the
Ottawa Sooners of the
Canadian Junior Football League. Marshall began his CFL coaching career with the
Saskatchewan Roughriders in 1994, spending the next six seasons with them as their defensive co-ordinator and
defensive line coach. In 2000, Marshall spent the next five seasons with the
Edmonton Eskimos, initially as their defensive line coach, then later as their defensive co-ordinator. In 2005, Marshall served as the defensive co-ordinator and assistant head coach for the
Ottawa Renegades. This season would ultimately end up being the Renegades final season before the team suspended their operations. In 2006, Marshall joined the
Winnipeg Blue Bombers as their defensive line coach and defensive co-ordinator, a position he held for the next three seasons. On January 13, 2009, the Hamilton Tiger-Cats announced the hiring of Marshall as their new defensive co-ordinator and assistant head coach. 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. After a 1–7 start to the 2011 season, the Roughriders fired Marshall on August 19, 2011. On January 25, 2013, Marshall was named the defensive coordinator of the Edmonton Eskimos. Marshall served as the defensive coordinator for
Queen's Gaels football from 2014 to 2017. His defense found success throughout his tenure, including an OUA conference leading 16 fumble recoveries in 2014 and the conference's second best pass defense in 2016. On January 3, 2018, Marshall became the head coach for the
Toronto Varsity Blues football team of
U Sports. After missing the playoffs for two seasons followed by a cancelled 2020 season, he led the Varsity Blues to a playoff berth in
2021 with a 3–3 record. 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. After regressing to a 2–6 record in
2023, it was announced on November 23, 2023, that Marshall would not return as the team's head coach. On April 10, 2024, it was announced that Marshall had been hired as the
defensive line coach for the
Ottawa Redblacks. He spent one season with the team but was not retained for the 2025 season. It was announced on March 21, 2025, that Marshall had joined the
Toronto Argonauts as the team's defensive line coach. He served in that capacity for one year, but was not retained in 2026. ==CFL coaching record==