He also played for the Indianapolis Colts of the NFL and the Montreal Alouettes, BC Lions and Toronto Argonauts of the CFL.

[1] As a senior in 2006, he led his team with 2,478 yards rushing for thirty-two touchdowns—including fifteen touchdown runs of fifty yards or more—and helped lead the Lakeland Dreadnaughts to their third consecutive Florida Class 5A state championship and second straight USA Today national championship.

[2] Following his senior season, he was a U.S. Army high school All-American and an all-state selection by the Florida Sports Writers Association, and finished his prep career with more than 7,000 all-purpose yards and ninety touchdowns.

As a junior in 2010, the Gators men's 4x100-meter relay team, including Rainey, Jeremy Hall, Terrell Wilks, and Jeff Demps, won the NCAA championship in the event with a winning time of 39.04 seconds.

[9][10] He debuted for the Steelers against the Denver Broncos on September 9, 2012 and scored his first NFL touchdown against the Cincinnati Bengals on October 21, 2012.

The Steelers waived Rainey on January 10, 2013, after he was arrested on a battery charge for attacking a young woman in a cellphone dispute.

Immediately following their Week 14 match-up, a losing effort to the Cincinnati Bengals, Indianapolis announced Monday December 9, that Rainey had been placed on season-ending Injured Reserve.

On December 5, 2016, Rainey and the Lions agreed to a two-year contract extension, keeping him with the club through the 2018 CFL season.

[19] Rainey passed 10,000 career return yards during the season, and was named Toronto's Most Outstanding Special Teams Player.

[20] Rainey was appreciative of the nomination, but stated that teammate Frank Beltre who led the league in special teams tackles was more deserving.

Rainey's older brother is former CFL, XFL and NFL running back and kick returner “He Hate Me” Rod Smart.