Chambers switched to rugby union from 2010 after signing a 2-year deal with the Queensland Reds to play in the Super 14. However, following a disappointing 2011 season - where he only started six of the Reds' 18 matches - Chambers was released by the club after missing a place in their thirty-man 2012 squad. He was named on the bench for the Reds Super 15 final victory over the Crusaders in 2011 – which featured fellow league-turned-union player Sonny Bill Williams on the opposing side – but did not play in the match.
Chambers signed for Pro12 side and former European Champions Munster in September 2011 on a short-term deal. He arrived to join up with Munster in October 2011. He played for Munster A against Connacht A on 21 October 2011. He made his full Munster debut against Aironi on 28 October 2011. He made his Heineken Cup debut for Munster against Northampton Saints on 12 November 2011. Chambers scored his first try for Munster exactly a week later, in their second Pool One game away to Castres Olympique. He was named in the Munster A team to play Ulster Ravens in the British and Irish Cup on 20 January 2012. This was announced to be Chambers last appearance for Munster, as he was returning to Australia to take up a contract with rugby league team Melbourne Storm. Munster A won the game 9–20, securing a spot in the semi-finals. In his four months with Munster, Chambers made 8 appearances for the senior Munster team, including 3 Heineken Cup caps, and scored 1 try. He also made 3 appearances for Munster A.
By being part of the 2012 NRL Grand Final winning team, Chambers joined Peter Ryan, Brad Thorn and Sonny Bill Williams in winning both NRL and Super Rugby titles (though he did not play in the Super Rugby final). Chambers won his in consecutive years after winning with the Queensland Reds in 2011.