The 29-year-old Samoa international has made 39 appearances for the club and spent time out on loan with Dewsbury and Halifax since arriving on an initial 18-month deal from the Mackay Cutters in 2015.
Sio later signed a two-year deal, which was set to expire at the end of the 2018 Super League season, but he has now departed with immediate effect.
He said on the club’s website: “I have thoroughly enjoyed my time here at Wakefield, I learnt a lot as a player under both Brian Smith and Chris Chester. There is a good bunch of lads at the club who made me feel extremely welcome and at home and I will definitely miss the camaraderie within the team.
“I would like to thank the fans for their support, they welcomed me with open arms and even now when I walk around the town they stop me for a chat. I would have to say that Wakefield Trinity are a club with the most passionate fans.”