A number eight, Muir led the Chiefs during the 2001 and 2002Super 12seasons, earning New Zealand rugby's "Super 12 Player of the Year" award for his captaincy efforts in his first year in charge. He spent his entire provincial career with Waikato and was captain for part of their 21 successive Ranfurly Shield defences. In 2002, Muir became the 20th Waikato player to reach100games in their NPC semi-final win over Otago, then left at the season's end to play rugby with JapaneseclubSanix. He played seven years with the Fukuoka-based club before retiring in 2008.