Melbourne Storm three-quarter Mahe Fonua will join Super League side Hull FC on a three-year deal from the start of next season.
The 22-year-old is a prolific scorer with the Storm, his hometown club, running in 23 tries in 50 NRL games.
The Australia-born back has played four times for Tonga, scoring twice.
"This is not just a coup for the club, it's also a coup for the competition," said Black and Whites head coach Lee Radford.
"We were surprised to hear about his availability as a relatively established NRL player and it certainly shows we're moving in the right direction in terms of our recruitment."
Hull have already signed Newcastle Knights stand-off Carlos Tuimavave, Canterbury back-rower Frank Pritchard and Wigan prop Scott Taylor.