The 30-year-old, who has also featured forthe Central Coast Rays and Eastern Suburbs in Sydney, started out in rugby league, but later switched to union.
Fainga'anuku signed for Glasgow in September 2012 on a short-term contract, but after impressing extended his stay to the end of this season.
Head Coach Richard Hill is delighted with his latest signing and believes the loosehead will be a powerful acquisition for Warriors.
"We looked at a number of props and there were several looseheads in the market and available," revealed Hill. "However, when all the coaches sat down and looked at video, it was very clear that Ofa was the one who made us all stand up. We quickly realised there was something special about him. He has that X-Factor.
"He is a big man but moves very quickly, a dynamic ball carrier and very good in defence which comes from his rugby league background.
"Ofa has grown up playing rugby league so has soft hands and likes to pass out of the tackle, but he also has a huge work-rate and the ability to tackle and get back in the line quickly.
"It's vital that he can be strong in the scrum for us week in and week out. He has learnt very quickly from his spell in the RaboDirect PRO12 and impressed us in the set piece in games against Ulster, Cardiff Blues and Newport Gwent Dragons," added Hill.
"Ofa is a very powerful man and will be one of the strongest in our squad. The strength and conditioning staff are naturally very excited about working with him.
"He has been to Sixways to see what we are all about and is now very keen to join us. He has been playing at a very good standard in Glasgow, with the Warriors topping the RaboDirect PRO12, and he is an international who wants to become a regular for his country.
"Ofa is an exciting signing for us and we are looking forward to him becoming a Warrior at Worcester."
Watch the new man in action. Click HERE to watch Ofa!