Since making his NRL debut in the opening round of the 2011 campaign, the 24-year-old fullback-wing has been plagued by a series of injuries as well as surgery which has limited him to just 25 first-grade appearances, from a possible 121 games, in five seasons.
Fisiiahi scored 15 tries in those 25 games but played just four games in 2011, four again in 2012, 11 in 2013, five last year and only one this season.
He made a belated start to the 2015 season following shoulder surgery in the offseason.
The Chiefs confirmed that Fisiiahi has signed a two year deal with the franchise, and will also be joining Counties Manakau in the ITM Cup.
Fisiiahi is the second Warriors player to make the code switch in the last month, with former centre-winger Ngani Laumape having signed on with the Hurricanes for next season.
Fisiiahi, a former Wesley First XV product, was tipped for a big NRL career after he scored 22 tries in 29 games for the Junior Warriors and helped them to the club's maiden NYC premiership in 2010.
"There has never been a question about Glen's ability. He's a hugely exciting player when he's fit," said Warriors coach Andrew McFadden.
"We've seen glimpses of what he can do, like the four tries he scored against the Tigers in Wellington last year.
"It's been frustrating for him, though, because while the potential was obviously there he just hasn't been able to get on the field often enough and he has now decided he wants to have a shot at rugby union instead.
"Glen is disappointed rugby league hasn't worked out the way he'd hoped and so are we. We'd all been hoping he would come through his setbacks but it wasn't to be. We wish him all the best in rugby union and we'll certainly be watching his progress with interest."
