On graduation she joined the BBC's trainee reporters scheme. She then joined BBC Radio Cleveland as a reporter for three years, before becoming a news presenter, and then co-presenting the drive-time show. She then joined BBC Radio 5 Live as a regional North East reporter, before relocating to London as a weekend news presenter, and also presenting on Newsbeat.
Foster joined the BBC Radio 5 Live Weekend Breakfast show on 23 April 2011, replacing Rachel Burden who moved to the weekday 5 Live Breakfast team alongside Nicky Campbell on 3 May.
On 14 November 2012, Anna became the Wednesday to Friday co-presenter of 5 Live Drive (4-7pm) alongside Peter Allen; Louise Minchin was the Monday and Tuesday co-host. Foster subsequently became the permanent co-host, alongside Livesey who replaced Allen in October 2014.