Earl, who joined the Panthers after leaving the Sydney Roosters at the end of 2009, has signed with the Raiders until the end of 2013.
The 22-year-old, who missed most of last season with a shoulder injury, said he was looking forward to a fresh opportunity at the Raiders after struggling to make an impact at Penrith.
"I'm very excited about joining the Raiders and I can't wait to get down to Canberra and start working with David Furner and the players," he said in a statement.
"It was a very hard choice to leave Penrith and Windsor as they have been great to me but for the future it was the best option."
Raiders chief executive Don Furner welcomed the arrival of Earl, as Canberra battles an injury crisis which deepened further following Josh Dugan's ankle injury against North Queensland last weekend.
"With our injury toll at the moment it's great to be able to sign a player with Sandor's experience for the rest of this season and next," Furner said.
"He will join the team as soon as he can and it's up to him to put his name forward and work his way into the NRL team."