Smith plays for the Hurricanes in Super Rugby, and also for Wellington in the ITM Cup. He made his Wellington debut in 2003, and was signed by the Hurricanes in 2004. Smith's Hurricanes career has been plagued by injury, and having been injured in 2006, 2007 and 2011, he made just 66 appearances in his first eight seasons with the side. He is the current Hurricanes captain, having led the side for the first time in 2007 in place of the injured Rodney So'oialo.
He made his All Blacks debut age 22, versus Italy in 2004, after a meteoric rise which saw him make his professional debut just a season earlier. In 2007, Smith faced a number of setbacks, mostly involving injury. However, he eventually earned his way back into a starting position, and by 2008, was the first choice centre for the All Blacks.
Smith was a member of the 2011 Rugby World Cup winning squad playing in the final against France at Eden Park in Auckland on 23 October 2011.
Against the Argentina on 28 September 2013, Smith and inside centre Ma'a Nonu achieved a record fifty international games together.
Smith took a six month break from rugby during the 2013 end-of-year tour, meaning he did not travel with the All Blacks squad to Japan and Europe.