Green made his first-team debut for Norwich City in 1999 and totalled 241 appearances across all competitions for them, making the PFA Team of the Year when they won the First Division in 2003–04. In 2006, he transferred to West Ham United, making the same number of appearances in a six-year spell in which he was their Player of the Year in 2008 and won promotion via the Championship play-offs in 2012. He then moved on a free transfer to Queens Park Rangers, winning the play-offs again in 2014. In July 2016, Green joined Leeds United on a one-year contract. He later joined Huddersfield Town and Chelsea for one year each before retiring in 2019.