His first Commonwealth Games came in 1994, in Victoria, British Columbia. He won a bronze medal in the singles and a silver medal in the pairs. At the Manchester Commonwealth Games in 2002, he won a bronze medal in the pairs, shooting with Jane Messer. He won HM the Queen’s Prize in 2002 and again in 2003, becoming the only person to win the prize in consecutive years.
Selected again for the Commonwealth Games at Melbourne in 2006, he shot in the full-bore rifle pairs competition in partnership with Dr Parag Patel (the youngest man ever to win the Canadian Open Championships). Together they took the Gold Medal. Barnett commented "None of this would be possible without the support of family, friends, psychologists, coaches, and work colleagues."
From 1990 to 1996, Barnett trained as a doctor at London's Charing Cross and Westminster Medical School, now the Imperial College School of Medicine. He was an Emergency Medicine Consultant at Charing Cross in London from 2006. , and has since moved overseas in 2009 with his family.
- Old Greshamian Club Address Book (Cheverton & Son Ltd., Cromer, 1999)
- A Recent History of The University of London Rifle Club (accessed 22 September 2007)
- Commonwealth Games results at bbc.co.uk (accessed 22 September 2007)
- Shooting for gold at bmj.com (accessed 22 September 2007)
- Home Nations Medallists at Commonwealth Games 2002 at sportinglife.com (accessed 22 September 2007)
- Some Recent Sporting Highlights: Shooting at greshams.com (accessed 22 September 2007)