Greening began his career in 1996 with York City, but moved to Manchester United in 1998, with whom he won the 1998–99 UEFA Champions League as a non-playing substitute in the final. However, he failed to make a breakthrough in the Manchester United first team and followed United assistant manager Steve McClaren to Middlesbrough in 2001. During his time at Middlesbrough, Greening earned his first call-up to the England national team, but he did not make an appearance. In 2004, he joined West Bromwich Albion for £1.25 million, and, in 2008, captained the team to the Championship title. Greening signed for Fulham in 2009 and helped them to the 2010 UEFA Europa League Final, before signing permanently the following summer. He signed for Nottingham Forest in 2011 and had a three-year spell with the club.