He made his maiden first-class hundred against Worcestershire in 2001, but two broken bones ruined his 2002 season and though 2003 was a better year there was little hint of the startling summer he was to enjoy with the bat in 2004.

In the 2006 season, he averaged 42.41 in the Liverpool Victoria County Championship and showed good form with the gloves and bat in one day cricket also.

In the winter of 2007–2008, Foster played for England Lions team for their tour to India, after being called up following an injury to Worcestershire's Steven Davies.

[4] Foster played for England in the 2009 ICC World Twenty20, receiving high praise for his sharp keeping and stumpings of Yuvraj Singh and Dwayne Bravo.

His continued form, particularly behind the stumps, was one of the factors that led to two promising wicket-keeper batsmen, Adam Wheater and Ben Foakes to leave the county to further develop their careers.

In 2018 he shared keeping duties with Wheater who had returned from Hampshire, and then Foster retired at the end of the season after hearing that Essex would not be renewing his contract.