The Samoan back can cover at full-back, winger or centre, and he joins York after two seasons playing in France, most recently with FC Lezignan after initially joining Baroudeur de Pia.
The 28 year-old previously played for North Sydney Bears in the New South Wales Cup.
York Knights head coach, Mark Applegarth said: "He's a player we've been monitoring for a month or two. He can fill in any of the positions in the back five.
"He's a real handful, a real unit. He's got some good skill on him, a really intelligent footballer.
"I'm sure he'll quickly become a fan favourite."
Mata’afa is available for Sunday’s Betfred Championship match against Hunslet at the LNER Community Stadium.
Yorkshireman leads Trinidad and Tobago bobsleigh team into Winter Olympics
Three Wins for York City Rowing Club at Tyne New Years Head
York City rowers claim three wins at Tyne New Year’s Head
Pickering Town Part Ways With Management Duo and Announce Succesor
Dan Pybus signs a two and a half-year contract with York City FC, committing his future to the club.
