The Fijian international, who has played nine games for the island nation to go with his 45 NRL appearances and 77 English Super League appearances, has made the decision to hop codes. He will join Perpignan.
Wiliame has already spent time in France, having played for the Catalans Dragons between 2017 and 2019.
While the signing of the now 28-year-old raised eyebrows at the time, he has become a fixture in the Dragons backline this season and is likely to remain there for the next few weeks at least. It comes as the Dragons battle suspension chaos caused by a house party which broke both NRL COVID protocol and a New South Wales public health order.
Wiliame has managed to cross for five tries in his eleven games this season, while also defending solidly.
Wiliame's departure adds to that of Matt Dufty, who has signed a contract with the Canterbury Bulldogs from the beginning of 2022. It frees up yet another roster spot for the Dragons, who have also ripped Paul Vaughan's contract up in the past week.
The Dragons were said to be open to an immediate transfer for Will Hopoate in a player swap with Matt Dufty, however, that appears to have cooled off with St Helens now reported to be the front-runners to secure Hopoate's signature.
Anthony Griffin's side have plenty of outside backs coming through their juniors though, with both Matt and Max Feagai, as well as Tyrell Sloan, likely to breakthrough into first grade in the coming 12 months.
Zac Lomax too, has been missing for a fair chunk of this season through injury, giving St George Illawarra ample replacements within their squad for Wiliame.