The 25-year-old Aucklander, who played in all three of Tonga's matches in the 2008 World Cup, has signed a one-year contract with an option for 2015 and will link up with new coach Lee Radford's squad for pre-season training subject to being granted a work permit.
A winger, full-back or centre, Talanoa scored 40 tries in 95 appearances for the Rabbitohs from 2006-12 and was tipped for a bright future in the game before suffering a life-threatening bout of pneumonia which put his career on hold.
"Hull FC have given me an opportunity and I'm really excited for it," he said. "I can't wait to get over there and represent the Black and Whites.
"For me it's about getting back into playing rugby league. League is where my heart is and that's what I enjoy doing but first of all, I've got to make the team and that's a battle I'm really looking forward to."
Radford said: "This is a great opportunity for him and one that could also prove to be an excellent signing for us.
"Fetuli was quite a player in the early part of his career, very strong, quick and powerful and someone that can play numerous positions, so it was surprising, although understandable, when he chose to take a period away from the game.
"I know a number of other clubs have been keeping tabs on him following conversations with agents and coaches over the last few months, particularly Brisbane who have looked at him a couple of times, so to come out on top despite competition like that it is very pleasing."
- Sports & Recreation