Peel started his rugby career playing for Tumble RFC at Under-8s level. He made his professional club debut for Llanelli RFC before moving to the Llanelli Scarlets region at its creation in 2003.
Peel made his international debut for Wales in 2001 against Japan. He was still on his geography degree course at the Swansea University at the time. During his time at Swansea University, he became friends with Edward Lewsey – a Welsh Under-21 international, and brother of England international Josh Lewsey. Peel has since scored five tries (25 points) scoring his debut Test try against Italy in 2003 for Wales, and has earned a total of 63 caps.
In 2005, Peel was selected for the British and Irish Lions tour to New Zealand, and was the youngest Lion on the tour. On 9 September 2007, Peel was captain for Wales when they beat Canada 42–17 in their opening match in the 2007 Rugby World Cup.