19th October 2017, 12:42 | Castleford
The 24-year-old will link up with the Grand Finalists after helping Rovers secure an immediate return to Super League.
"Mitch Clark is a player I have known for a long time having discussed his future with him three years ago," said Tigers head coach Daryl Powell.
"I'm delighted he has signed for Castleford at this time as I believe he has a big future with us.
"He is an all-action front rower who has great leg speed when carrying the ball and real intent when he is defending."
Clark grew up in New Zealand and signed for NRL outfit Penrith Panthers before enjoying spells with Doncaster and Bradford Bulls in England.
His switch from Hull KR to Castleford sees him return to West Yorkshire.
"I can't wait to rip into pre-season," said Clark.
"I was born in Pontefract and to get to play for this club and to play for Daryl Powell is such a massive opportunity for me."
Clark is Castleford's second signing of the week following the return of half-back Jamie Ellis, while prop Larne Patrick has left for Leigh Centurions.