He attended St. Edmund's College where he first represented the school's 1st XV aged 15.
His usual position is centre. He currently plays Super Rugby for the Queensland Reds. He was selected as vice-captain of the Australian Schools team in 2004.
The Fainga'a's are of Tongan and Aboriginal descent. Fainga'a was vice captain of the World Championship-winning Australian Under 19's in 2006. He also represented the Australian Under 21's in 2006.
Fainga'a made his Super 14 debut for the Brumbies against the Bulls in 2007 after recovering from a Lisfranc fracture in his left foot and added a further two caps during the season, coming off the bench against the Stormers and Sharks. A confident ball player and punishing defender, Fainga'a was called into the Australian Sevens side for the final two tournaments of the 2007 World Series in London and Edinburgh. He played in all eight matches for the Canberra Vikings in the Mazda Australian Rugby Championship, taking on the goal kicking duties at the back end of the season.
He joined the Reds Development Tour to Ireland and France at the end of 2008 and made his full Reds debut in 2009. At the start of the 2010 season, he lined up as the Reds' starting No. 12. Fainga'a made his test debut for Australia against the All Blacks in Melbourne in 2010.