After graduating in 1964, O'Brien returned to Liverpool to become a founder member of the Everyman Theatre.[6] As well as acting, she worked as an assistant floor manager for the company.[7]
She played the part of Vicki in 38 episodes of Doctor Who from 2 January to 6 November 1965, starring alongside the original Doctor, William Hartnell. She has reprised the role in several Big Finish ProductionsDoctor Who audio plays. In 2022, 57 years after playing the role on screen, she appeared as Vicki in a short webisode made to promote the release of her first season on Blu-ray. She reprised the role again in the series Tales of the TARDIS.[8]
After leaving Doctor Who O'Brien found it difficult to find acting work on television, and worked as a supply teacher. Her next role was in the theatre, where she appeared in an Oxford Playhouse production of Volpone with Leo McKern and Leonard Rossiter.[9]
In 1974, she played Celia in "Panic", an episode of the BBC Radio series The World of Daphne du Maurier. The 1980s saw her teaching acting workshops in the USA. She also made a rare film appearance in the comedy She'll Be Wearing Pink Pyjamas in 1985, opposite Julie Walters. She received the Time Out Critic's Choice award for her production of Mike English's Getting In in 1986.[19]
O'Brien in 2009
O'Brien has also written seven detective novels: Close-Up on Death (1989),[20]Deadly Reflection (1993),[21]Mask of Betrayal (1998), Dead Innocent (1999), Revenge (2001), Unauthorised Departure (2003) and Every Step You Take (2004); all feature the character of Detective Inspector John Bright.[22]
