Kenny-Dowall lived in Ngaruawahia, New Zealand where he attended Ngaruawahia High School until he was 16 years old. As a junior he played for the Ngaruawahia Panthers. He was a New Zealand Warriors junior but was unwanted by the club before moving to Sydney in 2004. Kenny-Dowall was selected for the Junior Kiwis in 2006.
He was named in the New Zealand training squad for the 2008 Rugby League World Cup but was not selected. He has been announced in the 2010 Kiwis 'train on' squad for the Four Nations. Instead, Kenny-Dowall played for the New Zealand Māori which met the Indigenous Dreamtime team in a curtain-raiser to the 2008 World Cup.
Kenny-Dowall played for the Roosters at centre in their 2010 NRL Grand Final loss to the Dragons. He cemented his position in the centres for the Kiwis in the 2010 Rugby League Four Nations scoring three tries including one in the final. He combined with the great and talented Benji Marshall, Jason Nightingale and Nathan Fien to set up the series winning 79th minute try. Kenny-Dowall's fine form throughout 2010 saw him coming runner up to Marshall in the Rugby League World Golden Boot award, where he made centre in the team of the year.
In 2011 in was selected in the NRL All Stars team. Playing off the bench he scored a try in their 28-12 win.
He played in the Roosters victory in the 2013 NRL Grand Final, revealing after the match he had played for the length of the game despite breaking a tooth and fracturing his jaw in an early encounter in the match. The injury forced him to miss the 2013 Rugby League World Cup.