At the 2003 European Junior Championships he won a gold medal. At the 2004 Olympics, he won the bronze medal in the men's 1,500m freestyle, in a time of 14:45.95 (a British and European record). He also swam at the 2004 European Championships and the 2005 World Championships.
At the 2006 Commonwealth Games, Davies won the 1,500 freestyle and was third in the 400 freestyle. In 2008, he finished second in the 1500 free at the 2008 Short Course Worlds.
Davies represented Great Britain at the 2008 Olympics, swimming in both the pool competition and open water race. In the men's 1500m freestyle race, he finished 6th. In theopen-water 10K race in Beijing, Davies finished second in the new Olympic event. Shortly after finishing the event, there was concern for Davies' state of health as First Aid staff rushed to stretcher him off for medical attention. Davies told the BBC shortly afterward: "For the last part of it I was delirious, I wanted it so bad. I've given it everything - the stretcher at the end was a bit mad but I've got something to show for it. I felt a bit violated to be honest, people swimming all over me, and the last lap was a real struggle.".
Davies qualified for the Olympics 10K at the 2008 Open Water World Championships in Seville, Spain where he finished just .03 behind the winner.
- Swim Wales Hall of Fame recipiant 2012
- Olympic Games 2008 Silver Medalist - 10k Open Water
- Olympic Games 2004 Bronze Medalist - Men's 1,500m freestyle, in a time of 14:45.95 (a British and European record)