Byrne started his rugby career with Bridgend Athletic U8s and he later played for Tondu RFC, Bridgend, Llanelli and Scarlets. He is now playing his regional rugby with Ospreys.
 
Having represented Welsh Schools he went on to secure his first full cap as a replacement against New Zealand in 2005. Throughout the 2006 RBS 6Nations he was a regular starter and toured with the Welsh team to Argentina that summer. His first international points came against the Pumas that summer. 

Byrne was called up again for the 2006 Invesco Perpetual Series where he scored a try in the victory over the Pacific Islands.
Consistent selection continued through the 2007 RBS 6Nations and for the summer tour to Australia where he started in the first test in Sydney which Wales lost against Australia. Whilst named in Gareth Jenkins’ initial squad for the 2007 World Cup he failed to make the final squad to make the trip to France. 

With the arrival of Warren Gatland he was included in the squad for what would turn out to be the Welsh Grand Slamming season and featured in every game for that campaign, scoring three tries. Byrne continued to see himself picked as part of the 2008 Autumn games and in the 2009 RBS 6Nations campaign.