Career
His usual position was full-back, although he has played on the wing. Byrne started his career playing dual-code rugby, playing Rugby Union for Bridgend Athletic Reconstruction Finance Corporation. And Tondu Reconstruction Finance Corporation, and after being spotted playing Rugby League for Bridgend Blue Bulls, he signed for the Llanelli Scarlets.
He made his debut as a replacement against the All Blacks on 5 November at the Millennium Stadium. Wales lost 3–41. He has since played during the 2006 Six Nations Championship, and earned a further two caps in a mid-year series against Argentina.
His sole appearance in the 2006 Autumn internationals was on the wing against the Pacific Islands.
Byrne was a revelation in the 2008 Six Nations Championship tournament at full back and a key component of Wales" Grand Slam. While playing against Connacht in 2007, Byrne demonstrated his abilities as a stand-in kicker when he kicked two penalties and two conversions, after fly-half Shaun Connor went off injured. He scored tries against England and Italy in the 2008 Six Nations Championship.
Following his superb performances for Wales in the 2008 Autumn Internationals against South Africa, New Zealand, and Australia (which included a try against the latter), Byrne had been tipped not only for a place in the British and Irish Lions squad, but also a place in the starting 15.
This was confirmed on 21 April 2009, when Byrne, along with Ireland"s Rob Kearney, were selected as one of the British and Irish Lions" fullbacks for the tour. After the fourth tour match he was one of five players to be picked for three of them.
This was later overturned and replaced by a fine of 5,000 Euros leaving him free to play in Wales" opening defeat to England in the 2010 Six Nations Championship match at Twickenham. Given permission to seek a new club for the 2011-2012 season, Byrne signed a three-year deal to play for French club American Society for Microbiology Clermont Auvergne, where he will play his club rugby post the 2011 Rugby World Cup.
On 8 January 2014, it was reported that Byrne had agreed to join Newport Gwent Dragons from the end of the 2013-2014 season.
On 23 April 2015, it was announced Byrne was to retire from all rugby with immediate effect, after failing to recover from a shoulder injury.