The 6ft 5in, 18st Kite played for Canterbury-Bankstown Bulldogs in 2008 and 2009 before joining Melbourne, where he was released after making only three senior appearances in two injury-hit seasons.
The 24-year-old, a member of Tonga’s 2008 World Cup squad, becomes the Vikings’ 16th close-season recruit – subject to him receiving a visa.
Widnes coach Denis Betts said: “John is a big man and a good athlete and I’m confident he will do a great job for us.
“Moving to the other side of the world and to another competition isn’t an easy decision for a young man to make but John is looking forward to the challenge and is backing himself to make an impression on Super League.
“He’s been training with Canterbury back home and will arrive in good shape and ready for action.”