Saskatchewan received Willis and a conditional fifth-round draft pick in exchange for second (eighth overall) and fourth (23rd overall) round selections in the upcoming 2012 CFL Draft, as well as a conditional draft pick in 2013.
"Odell is arguably the best pass-rusher in the CFL," said Roughrider general manager Brendan Taman. "I'm very confident he significantly upgrades our club on the defensive side of the football."
The six-foot-two. 255-pound Willis began his CFL career with the Calgary Stampeders in 2009, when he signed on as a free agent before the season.
The 27-year-old Mississippi native was acquired by the Blue Bombers via trade midway through that season.
Willis enjoyed a career season in 2011, piling up 27 tackles and 13 quarterback sacks. That performance earned him accolades as an East-Divison and CFL all-star.
During his three seasons in the CFL, Willis has tallied 78 tackles, 34 quarterback sacks and three fumble recoveries.