Lafai, 24, who can play in the centres, was recently granted a release by the Canterbury-Bankstown Bulldogs after five seasons with the club.
The Toa Samoa international has represented his country on five occasions and has played 72 NRL games to date.
"Tim is an exciting player whose services became unexpectedly available in recent days and we are delighted that he has chosen to join the Dragons," said Dragons Executive Manager Football Ben Haran.
"He brings experience and strike to our backline and will fit well into our structures and Club".
This article first appeared on Dragons.com.au
