The 27-year-old centre left the DW Stadium earlier this month after the club agreed to his request to return home to be closer to his family in the Land of the Long White Cloud.
Gelling has spent the last few days training with the Warriors and has now earned a one-year deal at Mount Smart Stadium.
Coach Stephen Kearney believes signing the Cook Islands international is a real coup for the Warriors and has backed him to shine in the NRL.
“It’s a stroke of luck for us that Anthony has come back,” said Kearney. “He proved himself in the Super League and has immediately impressed us at training this week.
“We’re thrilled we’ve been able to add him to our squad. He brings size and some special skills, providing further depth and increasing competition among our outside backs.”