He began his professional career in rugby union, where he played for Saracens.
“I’m excited by how the Tigers are playing this season. I already know a few of the boys and I’ve heard nothing but good things about the place, the players and the coaches,” he said.
“I’m looking forward to having room for my own game to improve, and I feel that I can only get better under Daryl Powell.
“To be part of a club that is challenging for silverware and to be part of what they have built here will really be something special.”
Cook is also thrilled to be making a return to a club where he has previously played on loan, and is pleased to be heading back north.
“I had a very brief loan spell with Castleford Tigers back in 2008 and got to experience the atmosphere the fans create.
“I relish the chance to get playing out there and the move up to Yorkshire will be great for me.”
Tigers coach Daryl Powell believes that Cook brings vital leadership qualities to his squad.
“Matt Cook is a quality individual player. I have been hugely impressed with him this season as a performer and a leader throughout a tough season for London,” said Powell.
“His size and strength will be great for us next season and his ability to play in both front and back row is a great attribute.”