The former Super Rugby player can play at number eight or on the blindside and joins the Ospreys after impressing his new employers in two Heineken Cup games against them this season.
He made his International debut against Ireland in 2001 and has gone onto captain his country seven times, including the defeat to Wales at the Millennium Stadium in 2009.
"I'm excited about signing for the Ospreys and what looks like an exciting challenge ahead," said Stowers.
"I've spoken at length to the coaches about their vision for the team, had a good look around the first class facilities there, and I'm really looking forward to being able to play a part in what they are trying to achieve.
"I've played against the Ospreys twice this season so I know a bit about the squad there, and from what I've seen of them over the last few months in the LV= Cup and the Magners League, there's strength in depth with some really good youngsters coming through that I can help develop.
"It's a fantastic opportunity for me to be part of a forward thinking and ambitious set-up, and it's an exciting move for me, personally and professionally, that will allow me to experience rugby in new environments."
Elite Performance Director, Andrew Hore, said:
"George will bring a real physical presence to our back-row, and as we experienced ourselves in the two games against London Irish in the Heineken Cup, he provides a real nuisance value, making life incredibly difficult for the opposition with his high work-rate.
"He is also a proven leader with experience of captaincy at international level, and we've no doubt that he will prove to be a real asset to the Ospreys over the next two years. As a player who has made a huge impact in England during the last two seasons, we are extremely pleased to have secured his services and we look forward to welcoming him to Ospreylia."