The Waikato flanker first made his debut for the All Blacks on 16 June 2001 against Samoa at Albany. He is known for his ability to steal the ball in the tackle. While he has been in and out of the All Black squad under the current coaching regime, he has continued to be a Waikato and Chiefs mainstay in his home town of Hamilton. Holah was instrumental in the NZ Māori's defeat of the British and Irish Lions during the 2005 tour at his home ground, Waikato Stadium.
In 2006, Holah was named in the unfamiliar position of blind-side flanker for the Ireland Test in Hamilton, his first start in the All Black jersey since 2004.
On 14 August 2007, it was announced that Holah had signed a two-year contract with the Magners League champions, the Ospreys. He enjoyed his time there, later signing a one-season extension on his contract. In the 2009/10 season he was named Ospreys' Coaches Player of the Year, having been named Man of the Match against the Leicester Tigers in a must-win Heineken Cupmatch with a heroic individual defensive display, which he reproduced multiple times in helping the Ospreys to lift the Magners League title that year.
On 18 April 2011 it was announced Holah would return home to play for Waikato in the 2011 ITM Cup. Holah became a regular member of the starting side.