Rees, started playing rugby at the age of 11 as a hooker for Tonyrefall U11s. Rees currently plays for the Llanelli Scarlets, having joined the region for the 2004 season. His previous clubs include Merthyr, Pontypridd and the Celtic Warriors. 

Rees made his Test debut for Wales against the USA in 2005 and won his second cap against Argentina in the summer of 2006. He then was selected in the the national squad ahead of the Invesco Perpetual Series in the autumn of the same year. He made the starting line-ups for the matches against Australia and Canada, and also featured as a replacement in the Series finale with New Zealand. 

Rees starred in the 2007 RBS 6 Nations as a replacement in both the tournament opener against Ireland and second match with Scotland. He also made the starting XV in the losses to France and Italy. 

Rees was named in the 30 man squad for the Rugby World Cup 2007. He made three appearances for Wales in France as he was included in the starting line-ups in the clashes against Canada, Australia and Fiji. He returned to international action in February 2008 in the RBS 6 Nations match against England. 

Rees was selected for Wales' 2008 autumn internationals, and started games against South Africa, New Zealand and Australia.
His performance for both club and country in 2009 has earned him a selection on the 2009 Lions Tour to South Africa.