In 1998 he made his Stormers debut, where in late April 1999, Muir suffered a serious neck injury against the Auckland Blues which led to the centre retiring in mid May of that year.
During this same period he had a brief stint with in the Northern Hemisphere with Newport RFC[4] before becoming head coach of the Sharks ahead of the 2005 Super 12 season.
In 2008, Peter de Villiers took over from Jake White as the Springboks head coach following their 2007 Rugby World Cup triumph, and appointed Muir as his assistant to look after the backs.
[5] With Muir's commitments with the Springboks during the international periods, John Mitchell joined the franchise and would lead the side during the 2010 Currie Cup campaign.
Muir therefore had his contract cancelled and on 2 June 2022 was named interim head coach of the Dutch national rugby union team.