Slack was a twelfth round draft pick of the Houston Oilers of the NFL in 1990, and remaned with them (mainly on heir practice roster) until 1992. Slack also spent some time with the New York / New Jersey Knights of the WLAF. Slack first came to Canada as a free agent signing by Winnipeg in December of 1992, but was released by the Bombers in July of 1993 before playing any regular season games for them. Toronto signed Slack as a free agent and he dressed in 11 games for Toronto in 1993. It was a fairly deent rookie season with a 56.5% completoin percentage and 1372 yards passing in just 184 attempts. In 1994, Slack was traded halfway through the year (September) to Hamilton for DB Joe Fields and LB Glen Young. Slack signed as a free agent with the expansion Birmingham Barracudas in 1995, but was traded early in the season to Winnipeg to compelte an earlier deal. 1995 was Slack's mos productive year to date as he threw 302 passes for 2007 yards. Slack remained with the Bombers in 1996 and became a free agent in February of 1997. He signed with the Saskatchewan Roughriders and played three seasons for hte Green and White. HIs second season in 1998 was his career best with 463 attempts of which he completed a very good 62.0% for 3721 yards. Slack was released by the Riders following the 1999 season, but returned to the CFL in 2002 to play 11 games with Toronto and then 3 games for Hamilton in 2003.