The 29-year-old, who can play at prop or loose forward, will join the Vikings ahead of the 2018 season.
Widnes head coach Denis Betts, whose side currently sit third in the Betfred Super League Super 8s Qualifiers table with two matches remaining, is delighted to finally land a long-term target who has been selected for State of Origin honours with New South Wales in 2013 and 2015.
He told the club's official website: "We have been interested in Will for some time, so I am very pleased to have secured this deal.
"Will is a quality player and will add a lot to the team with his experience of playing in the NRL. He is strong and carries the ball well, but can also offload and support attacking plays effectively too.
"I have also been impressed by his character and his excitement for taking on a new challenge at Widnes Vikings. I'm looking forward to him linking up with the team next season."
Matthews has played 93 games in the NRL for Gold Coast Titans and the Dragons and is also a former youth international for Australia.
The versatile forward said: "I'm delighted to be joining Widnes Vikings. I've always been interested in playing in the UK, so it is great to have this opportunity to do so at the Vikings."