The 24-year-old back rower, younger brother of Castleford centre Peter Mata'utia, was released by the Knights from the last year of his contract to enable him to link up with his old coach Kristian Woolf at the defending Super League champions.

"Sione is a terrific person and I know that because I have coached him," said Woolf.

"He is a real good trainer and professional in regard to how he goes about his work.

"He is a good player and we see him as a bloke who can come in and play in the forwards for us and give us some real speed around the ruck as he has a good skill level.

"He can also play on an edge and offer us some 'punch' out there. He is a real strong defender too and he ticks a lot of boxes for us on and off the field."

The capture of Mata'utia follows that of Joel Thompson and Agnatius Paasi as Woolf plugs the caps created by the impending departure of Zeb Taia, Dominque Peyroux and Joseph Paulo.

Mata'utia made his debut for the Knights in 2014 and later that year became the youngest player to represent Australia, at just 18 years and 129 days, eclipsing the record held by Israel Folau by 65 days.

He captained his club at the age of 20 and went on to play three Tests for the Kangaroos and another for Samoa.

"I am really excited," Mata'utia said. "I have been at the Knights since I was a junior so it was hard to leave but it is an exciting move.

"I have heard nothing but good things about Saints from my brother and if I was moving to England, it was definitely to Saints.

"I love the pressure of always trying to be the best and at the top is what excites me. People expect Saints to be at the top and I can't wait to be a part of it.

"I have known Kristian Woolf for a long time since he coached me at the Knights and I have got along with him really well."

Australian Associated Press