Gale, 26, will help to fill the void left by Salford loanee Marc Sneyd, who is moving to Hull once his loan deal with the Tigers finishes at the end of the season.
Former Leeds, Doncaster and Harlequins scrum-half Gale is the club’s sixth new signing for next season, and the second half-back, following the capture of Samoan international Ben Roberts from Melbourne.
He said: “I am really excited to be here. Castleford have had a great season, and Daryl and his team around him have fulfilled the potential, and they have turned Cas into a proper team.
“I am jumping at the opportunity and I cannot wait. Daryl showed a bit of interest, and I have worked with him at the England Knights and at Leeds before. I like how he goes about things, and even though there was other interest, once I spoke to Daryl that was it – I wanted to join Castleford.”
Powell said: “I am delighted we have been able to secure the services of a quality half back who not long ago was just on the edge of international recognition. Luke’s organisational ability alongside his willingness to both play at the defensive line and indeed through it will fit neatly into how we want to play next season.
“His passing and kicking game are top quality. Luke alongside Ben Roberts and Liam Finn give us variety and quality at half back with Ben Reynolds proving he can also step up when needed, giving us additional depth in such a pivotal position.”