The powerful Australian - an NRL Grand Finalist with Storm in 2016 - has joined on a three-and-a-half-year contract.
Blair, 27, should help solve Castleford’s problematic right centre slot where head coach Daryl Powell has tried four different players already this term.
At six foot four inches and weighing 16 stone, the former Parramatta Eels and Manly Sea Eagles player offers a considerable presence.
“Cheyse’s signature is a huge statement of intent for the Tigers going forward,” said Wells.
“He is proven at the highest level in the NRL and brings that experience and competitive edge to a progressive and motivated team.
“I am confident that Cheyse will be a huge addition to the Tigers squad and we are all looking forward to seeing him in a Cas shirt just as soon as the visa paperwork is completed.”
Blair, who missed out on Melbourne’s 2017 Grand Final success due to an ankle injury, said: “I am really excited and pumped to be joining the club.
“I am looking forward to getting over there, meeting everyone and ripping in.
“I know Castleford have the best rugby league community and fans and I can’t wait to hear their roar!”
The player has 18 tries in 38 games for Storm but has not featured this season.
Powell added: “Cheyse is an experienced outside back from probably the best club in Australia.
“As such, we know we are getting a quality performer with bags of experience and ability.
“I’m looking forward to welcoming him and his family to the Tigers and I am confident he will add to our quality both on and off the field.”