Setaimata Sa has agreed an 18-month deal with Hull FC, ending a spell in rugby union with London Irish.
Sa, who can play in the back row as well as in his usual position of centre, joined the Exiles in January 2013 but made only four appearances for the club because of injuries.
"I am really looking forward to getting back playing rugby league - the game where my career started," he said.
Sa, 26, played for Sydney Roosters before joining Catalan Dragons in 2010.
The dual rugby league international has scored 24 tries in 69 matches in Super League and five in as many international appearances for Samoa.
Sa, who also played for New Zealand in the 2008 World Cup final win over Australia, is set to make his Hull FC debut in Friday's Super League game against Leeds at Headingley.
Meanwhile, winger Jason Crookes has been given a two-match ban after being found guilty of making a careless high tackle on Hull Kingston Rovers player Liam Salter in Saturday's derby defeat.
Crookes, who was sent off for the challenge, will now miss the away games at Leeds and London Broncos.