The 33-year-old rejoined Trinity from Huddersfield ahead of the 2017 season and scored eight tries in 29 appearances as Chris Chester’s side finished fifth in Super League.
“Scott is an influential player both on and off the field,” said Chester. “He played a large part in the success that we had on the field last year and I look forward to working with him for the next two seasons.”
Grix spent the 2008 and 2009 seasons at Belle Vue before enjoying a seven-year spell with the Giants.
“I really enjoyed last season, especially with how well we did,” said Grix, who finished the year representing Ireland at the World Cup.
“The signings the club have made along with the re-signing of key players, it shows how far we have come and I am excited to be involved in the next couple of years.”
Meanwhile, forward Mikey Sio has left the club by mutual consent.
Sio joined Trinity from Queensland Cup side Mackay Cutters in June 2015 and became a first-team regular.
But he made only nine appearances last season and finished the year on loan with Championship club Halifax.
“I have thoroughly enjoyed my time here at Wakefield,” said the 24-year-old. “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.”
Chairman Michael Carter added: “I would like to thank Mikey for his service to the club since arriving at a difficult time in 2015.
“His contribution was invaluable at that time and I wish him every success in the future.”