"He is certainly an exciting prospect for us and his attacking ability will fit in with the style and brand of rugby we seek to play. He's impressed with his pace and will provide us with some new options," said Scarlets head coach Nigel Davies.
"We are delighted Viliame Iongi is joining us - I think he will give us an exciting new dimension. Along with Sione Timani, we've now secured some new strike players in key positions who will help anchor our squad as well as add to the dynamic and energy in our team - which in turn, will have a positive influence in bringing on younger players in our squad."
The first two rounds of European action may come around too soon for the winger but he is looking forward to a new challenge with the Welsh region.
"It's is a great opportunity for me and as my first professional rugby contract, I'm now going to get the chance to play in Europe and hope the way I play will fit in well with their style," he said.
He added: "I'm looking forward to being part of such a professional set-up and will give it everything I can. The Scarlets play great rugby and I'm looking forward to being part of the team."
The Scarlets first Heineken Cup game this season is against Castres Olympique at Parc y Scarlets on Saturday November 12, before they travel to last season's beaten finalists the Northampton Saints the following weekend.