The capture of the NRL star is a major boost for Daryl Powell’s side given a raft of clubs were interested in the Tonga international once it became known he wanted to move overseas next season.
A strong ball-carrier and excellent finisher, he has scored 62 tries in 139 games for Cronulla since debuting in 2013.
Importantly, Auckland-born Feki knows what it takes to lift a title, too, having been part of the Sharks side that won the 2016 Grand Final.
“I’ve been at Cronulla for seven years now,” said the former Junior Kiwis international.
“I’ve been comfortable here but this is a new chapter in our lives and my partner and I are really excited to come across to Castleford and to Super League.
“It’s going to be a new challenge but Cronulla play an attacking style of rugby as well so hopefully I can bring that over there.
“I’ve played with Junior Moors at the Sharks and I know Jesse Sene-Lefao already as well.
“I’ve been messaging him and he’s been tipping me up on the club and what it’s like.”
Feki, 28, added: “As a player, I just try to do my job for the team and finish any opportunities that come my way.
“I’ve played a lot of my games with the Sharks on the left but I’m also really comfortable on the right and I played on that side at the weekend.
“I’m not bothered where the coaches want me to play, wherever they put me I’ll come across and do my best for the club.”
Feki’s capture follows on from Castleford’s high-profile signing of Melbourne Storm centre Cheyse Blair who arrived in April and, theoretically, they could form Tigers’ right-edge partnership in 2020.
Castleford director of rugby Jon Wells says the club has been watching the player closely for more than a year.
“Sosaia has been a consistent performer in the NRL with Cronulla Sharks and will bring pace and power as well as NRL Grand Final-winning experience to our squad for 2020 and beyond,” he said.
“He is a humble guy and whilst we recognise he has a job to finish in order to leave Cronulla and the NRL in the best way possible, I know that he is also excited that he and his partner will have a new chapter in their lives to look forward to, starting in November.”
Powell added: “Sosaia is a player who has been performing at the top level for a number of years in the NRL.
“He was a part of the Cronulla team that won the title in Australia which means that our last two recruits from overseas know what it takes to win a championship.
“He is big, strong and aggressive with the ball and an experienced defender. “Our back line for next season has a real look of ability about it with strong competition for places in all positions and Sosaia adds hugely to our quality.”