Joseph was the Riders' quarterback when the team won the Grey Cup in 2007. He was named the league's Most Outstanding Player that season.
He was traded to Toronto in 2008 and finished his career with the Edmonton Eskimos.
He announced his retirement in January.
The Riders have been without their lead quarterback since Darian Durant injured his arm at the Banjo Bowl in Winnipeg.
Tino Sunseri and Seth Doege have filled in with mixed results.
The Riders announced Kerry's return in a tweet, but didn't immediately elaborate on what capacity he'd be back as.
More to come