
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.