Sanderson was first capped on England's 1998 southern hemisphere tour as a 20-year-old, facing New Zealand twice and South Africa, and he won another three caps on the 2001 tour to North America, during which he scored a try against the United States.[3]
At the end of the 2003–04 season he moved to newly promoted Worcester Warriors, as captain, he was instrumental in ensuring the Warriors remained in the Premiership. He started every Premiership game last in 2004/5 and Sanderson was nominated for Zurich Player of the Season 2004–05 and the PRA Players' Player of the Year. This consistency resulted in an England recall for the autumn test opener against Australia in November 2005. Despite some impressive performances in the 2005 autumn internationals and being made captain for England's tour to Australia in 2006, he fell out of favour with England when Brian Ashton replaced Andy Robinson as coach in late 2006 and did not feature since.
Sanderson is an established and firm favourite at Worcester Warriors – both of the supporters and the club, and is fondly referred to as 'Captain Fantastic'. He has played over 100 top flight games and scored 22 tries for Worcester and has again being named as club captain for the 2008/09 season by Director of Rugby for Worcester Mike Ruddock.
Sanderson was also a high-calibre sevens player, having made his debut back in 1997 in Hong Kong. In 2003–04 he played in six of the IRB World Series rounds including the three wins in South Africa, Hong Kong and London. He also helped England win the prestigious Hong Kong event. In 2002 he was also a member of England's Commonwealth Games squad in Manchester.
Sanderson is the Chairman of the Professional Rugby Players' Association and he is well placed to understand the problems players face, particularly with injuries. A fractured shoulder, two damaged knees and prolapsed disc have all kept him out of the game at different stages. Sanderson is also now the players representative of the This is Rugby campaign, in association with The Professional Rugby Players' Association, Premier Rugby Limited and the RFU, to promote the Core Values of rugby following a spate of disreputable incidents in professional premiership rugby.
Sanderson committed his future to Worcester Warriors on the eve of the 2007/08 season by agreeing a new two-year deal, which would see him remain at Sixways until 2010.
In August 2011, Sanderson was forced to retire from rugby after failing to recover from a shoulder injury.[4]
