Shillington, 24, was a priority signing for the Raiders following the departure of Michael Weyman next season to St George Illawarra.
His long-term deal shows the faith Canberra officials have in his ability to lead their forwards well into the future.
Shillington had been hopeful of remaining at the Roosters but salary cap constraints forced him to look elsewhere and he is now excited about a move to Canberra.
"The Raiders are a young side on the up, and after talking with Nigel Plum and Joel Monaghan it looks like they have a strong future," Shillington said.
"They have a good young side with plenty of talent, and their Toyota Cup team is also strong at the moment.
"I'm looking forward to moving to Canberra next year, but until then I'll be looking to finish the season strongly at the Roosters."
Raiders assistant coach David Furner, who will assume head coaching duties in 2009, said the signing of Shillington was a huge boost for the club.
"Front row is a position we've been looking at boosting, and I think his signing is a very good one for the club," Furner said.
"His size, his aggressiveness, his off-load ability and ball playing ability makes him a great asset.
"He's still young, and he'll add a bit of starch to the pack."