[2] Westley's Essex career began in the 2004 Second XI Championship where he played his debut match as a 15-year-old against a Middlesex side captained by then 51-year-old ex-Test cricketer John Emburey.
Westley continued to play occasionally throughout 2004 and 2005, also two matches in the Minor Counties Championship for Cambridgeshire in 2005.
In September 2009 Westley scored his first century for the first team reaching 132 against Derbyshire.
After playing for the England Under-19 cricket team, including at the 2008 ICC Under-19 Cricket World Cup in Malaysia, Westley was added to England's Test squad ahead of the third Test against South Africa in July 2017 batting third as a replacement for the injured Gary Ballance.
A series of low scores meant that he dropped out of the side after the end of the 2017 English summer.