"We have deliberately looked for high quality, international players in key positions and in John, we believe we've got it absolutely right," said Ulster's Operations Director David Humphreys.
"He's a hugely talented player, both at set piece and in the loose, and he will bring a huge amount of Super Rugby and international experience to Ulster."
Since joining the Auckland Blues in 2004, Afoa has made an impressive 86 Super Rugby appearances and in 2005 he became the 1062nd player to represent the All Blacks when he made his first senior appearance against Ireland.
Prior to gaining senior recognition, Afoa represented New Zealand at Schools, Under-19 and Under-21 level.
In 2003, he was part of the New Zealand side which won the Under-21 World Championship staged in England and was one of four New Zealanders named in the IRB Team of the Tournament.
He has made 28 appearances to date for the All Blacks, most recently against Scotland last November and looks certain to be part of the squad for this year's Rugby World Cup which will be held in his home country.
Commenting on his move, Afoa said: "I've been part of the Blues family for my entire career so far and so, when the opportunity to look at a move came up, I felt that period post World Cup would be the perfect time.
"I've done my research and can't help but be impressed at how the Ulster squad is developing. There seems to be a good mix of local and overseas players and I'm very much looking forward to playing my part in that.
"I want to challenge myself and the northern Hemisphere style of play will certainly offer me that.
"Most of the players moving north state that the chance to participate in the Heineken Cup is one of the key factors in their decision and the same is true for me.
"But since the possibility of a move came up, I've also caught some of the Magners League and that looks like a competition that is going from strength to strength.
"From what I hear, the Ulster people seem to have a similar outlook as Kiwis and I've been told that I can expect a warm welcome when I arrive in Belfast.
"I have a young family who will be making the move with me and while the opportunity to experience a new culture and way of life will be a wonderful experience for all of us, it's nice to know that we won't feel too far away from home."