"I'm delighted to be joining Widnes Vikings," Gelling told the Viking's website.
"Looking at the talent at the club, their players who have re-signed, and the young lads who are coming through, I believe that the Vikings have real potential for the seasons ahead.
"Before signing this deal, I spoke in length to (club CEO) James Rule. He shared the club's vision for the coming seasons and I'm very excited to have the opportunity to be part of this.
"Widnes Vikings have had a tough season this year, but I know that we can turn this around. I am looking forward to linking up with the boys next year in 2019 and to making a difference to the side.
"I know from experience that the Vikings have brilliant supporters and I can't wait to get out in front of them next year. I'm grateful to everyone that continues to get behind the boys this year and look forward to wearing black and white next season."
Widnes' interim head coach Francis Cummins was excited the club had managed to snare the rangy centre.
"Anthony is a tremendous signing for the club," said Cummins.
"We've been working really hard to find a calibre of player who will enhance our team, and I believe that Anthony is that type of player.
"Anthony has been one of our top targets, as we have planned for next season, and James Rule has been in regular conversation with him over the past couple of months to help make this deal happen.
"Anthony has an 'X Factor' about him, with the ability to produce something out of nothing in a way that few others in the modern game can replicate. Players of his quality are few and far between, and we are excited that he will be representing our club."
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