Kelly comes to Canberra with plenty of top flight Rugby League experience, after previous stints with Balmain, the Dragons and the Sharks.
The 23-year-old Kelly said he is looking forward to a new home in the nation's capital, and is excited about joining the Raiders ranks.
"The Raiders are a great club who are going to go places and I am hoping to be a part of this," Kelly said. "They seem very professional and I can't wait to get down there and start playing with them."
Kelly had a great start to the 2006 season for the Sharks before injuring his shoulder, scoring an impressive 11 tries from his 11 appearances.
Originally from Eden on the NSW South Coast Kelly already has a connection with the Raiders, as he used to line up against Raiders prop Michael Weyman in the South Coast junior grades.
"I was a year older than Mick but I certainly remember playing against him," he said. "I am looking forward to playing with him rather than against him."
Raider's general manager Don Furner said Kelly will be a good addition to the Raiders line-up for next season, and will add some solid depth to the Raiders playing ranks.
"Brett is ready for a big season and we are confident he will have that with us next year," Furner said. "He has shown some promising signs this season at the Sharks and we are excited about him coming onboard."