Born in Clacton-on-Sea, Westlake progressed through the youth ranks at Ipswich Town, signing professional forms with the club during the summer of 2002. Westlake made his debut for Ipswich, coming on as a substitute in a 1–0 home defeat to Gillingham on 26 October 2002. Westlake made a further three appearances for Ipswich during the 2002–03 season. During the 2003–04 season, Westlake made a further 43 appearances for Ipswich and also scored 7 goals, the first of which came during the 3–4 home defeat to Gillingham on 1 November 2003. In August 2004, he was called up to the England Under-21national team. Westlake made a total of 125 appearances for Ipswich, scoring 17 goals.
Leeds United
On 4 August 2006, Westlake transferred to Leeds United for a fee of £400,000 plus the transfer of former Brightonleft-backDaniel Harding to Ipswich in a part-exchange deal. Westlake made his debut on 5 August 2006, coming on as a substitute during the 1–0 home victory over Norwich City. In total, Westlake made 29 appearances for Leeds during the 2006–07 season, in which the Yorkshire club were relegated from the Championship. During the 2007–08 season, Westlake made 23 appearances for Leeds and scored his only league goal for the club when netting the last-minute winning goal in a 1–0 away win at Oldham Athletic on 2 October 2007. He had earlier scored his first goal for Leeds in a 1–0 win at Macclesfield in the League Cup on 14 August 2007.
On 3 March 2008, it was revealed that Westlake had agreed an initial one-month loan deal at League One play-off rivals Brighton & Hove Albion. On 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. In total, Westlake made 11 appearances for Brighton, scoring two goals.
Cheltenham Town
On 24 October 2008, Westlake joined League One side Cheltenham Town on an initial three-month loan deal. Westlake made his debut the following day during the 3–1 away defeat to MK Dons. During his loan spell at Cheltenham, Westlake played 14 games and scored 1 goal during the 2–1 away victory at Leyton Orient. On 24 January 2009, Westlake had his contract terminated at Leeds United by mutual consent. Later that day, Westlake signed a contract with Cheltenham Town for the remainder of the 2008–09 season. Westlake also scored on the day of his permanent debut for Cheltenham during the 2–2 home draw with Brighton & Hove Albion.
Oldham Athletic (loan)
With Cheltenham Town suffering from financial difficulties, Westlake joined League One side Oldham Athletic on loan for the remainder of the 2008–09 season on 19 March 2009. Westlake made his debut for Oldham on 25 March 2009, during a 2–0 home defeat to Tranmere Rovers. In total, Westlake made 5 appearances for the club.
Wycombe Wanderers
On 15 July 2009, Westlake signed a two-year contract with recently promoted League One side Wycombe Wanderers. He was released from his contract on 18 March 2011 and the following week joined Colchester on trial.
Montreal Impact
Westlake joined the Montreal Impact on trial starting 5 July 2011. He formally signed with the North American Soccer League team on 15 July 2011, his contract expiring after the 2011 season. Westlake quickly became a fixture in the Impact's starting lineup scoring two goals in 13 games. On 5 December 2011, it was announced that Westlake re-signed to continue with the Impact in 2012, the team's first year in Major League Soccer, however Westlake was waived by Montreal on 27 February 2012, despite appearing for the club during their pre-season.
Needham Market
After being released by Montreal Impact following the introduction of a "six foreign players" rule, Westlake returned to Suffolk before signing for Needham Market eighteen months later in June 2013.
