The Canadian has spent the majority of the past seven years in the AHL, most recently with Stockton Heat.
Before turning professional Riley iced for Ferris State University in the NCAA for four seasons.
Riley said: “Belfast seemed like a perfect fit and a great opportunity that I could not pass up. I’m a bigger, physical forward and I like to play a well-rounded game.
“I was more of a scorer when I played NCAA and when I transitioned to the pro game, I was more of a ‘bottom 6’ forward and was expected to play more of a physical brand of hockey, which is something that I will never shy away from.
“With the opportunity to play for the Giants, I hope to add a scoring punch also.
“I’m looking forward to playing in front of the Belfast fans and I know we’re looking forward to putting a good product on the ice for them.”