The 28-year-old joined the Belle Vue club from New Zealand Warriors at the start of last season, and missed just two games in the Wildcats’ successful fight against relegation.
"It is a blow but it was anticipated and it now allows one of our young players to step up to the mark," said Wildcats chief executive Steve Ferres.
"Although it leaves us short of cover, we have options at loose forward and in the back row."
Betham missed two engage Super League games after a suspension for fighting, but was still a vital component of the Wakefield side during his spell at the club.
Betham will start out in the cruiserweight division, but hopes to work his way down to light heavyweight; details of his first fight are expected in the New Year.
His father – also named Monty – was a professional boxer, fighting 53 times as a middleweight or light heavyweight between 1973 and 1982.