He arrives at the club with a high recommendation from head coach Tony Hanks who has kept an eye on his progress over recent years.
""He was a player whom I met when he was about 13 and he's always been a good player. He's come through the Auckland system like Sammy Tuitupou and Tasesa Lavea, so he knows those guys and will be familiar with them," said Hanks.
"He's got a big engine and has played for younger New Zealand teams. He's played a lot of Super 15 games in an Auckland side where he has been competing with very good All Blacks throughout his career. He comes from good stock. He's a leader and a very intelligent player, and his sister is a well known singer in New Zealand. I think he's talented musically off the field, too.
"We're confident he can fit straight in. When you are bringing someone in the middle of a season, you are looking for someone who can slot in seamlessly and that's what Onosa'i will be able to do.
"It's good timing for him, too, as he's had a few niggles over the past couple of years, so he hasn't had the consistent game time that he would have liked. It's nice fit for him as much as us, as we're going to get someone who is really motivated.
"This is not someone who is ending their career, this is someone who is looking at a new opportunity and who is really motivated to do well."
Sale Sharks kick off their 2011/12 Amlin Challenge Cup campaign with a trip to last season's quarter-finalists Brive on Saturday November 12 before welcoming Rugby Club La Vila to Edgeley Park the following week.