He was a trainee at Ipswich Town and signed as a professional in 2002. He won the coveted Player of the Year award in 2004. He moved to Leeds United in a part exchange deal for Dan Harding in August 2006. Westlake had featured in many of Leeds' matches in the 2006-07 Championship season, playing alongside the likes of Shaun Derry, Kevin Nicholls and Jonathan Douglas in central midfield.
Westlake admitted he was frustated at being sidelined with a groin injury and wanted to help the club avoid relegation. However, Leeds were relegated in May 2007.
On the 3 April 2008, Westlake, Leeds United and Brighton & Hove Albion agreed that the player would remain on loan at the Withdean for the remainder of the 2007/08 season. Leeds are now trying to offload Westlake as he is deemed surplus to requirements at Elland Road. Brighton is his likely destination.