Deakin earlier appeared in the television sitcom Oh, Doctor Beeching! (1996–1997), where she played the role of May Skinner, replacing Sherrie Hewson from the original pilot. She has also made many single television appearances, including playing Jill, the receptionist from Pear Tree Productions, in one episode of the first series of I'm Alan Partridge, a rural dominatrix in Doc Martin as well as roles in Midsomer Murders and Coronation Street. She appeared in the Sketch comedy series Big Train alongside fellow Spaced cast members Simon Pegg and Mark Heap. She plays Dr. Jean in the Alan segments on Modern Toss.

On television, Deakin played Stella Tulley in Side by Side and Marsha, the ageing divorcée landlady, in the British sitcom Spaced (1999).

Deakin had a cameo in the feature film Shaun of the Dead (2004) and played the pub landlady Mary Porter in the film Hot Fuzz (2007) by Simon Pegg and Edgar Wright. In 2009 she was cast as Maggie, a Brighton mother in Ben Wheatley's British crime film Down Terrace. She later appeared in Ben Wheatley's 2015 cinema adaptation of High-Rise as Jean, the assistant to protagonist Dr. Laing.