Maureen O'Brien (born 29 June 1943) is an English actress and author best known for playing the role of Vicki in the BBC science fiction television series Doctor Who, although she has appeared in many other television programmes as well.

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. Over 40 years later, she reprised the role in several Big Finish Productions Doctor Who audio plays.

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.

She had a recurring role as Morgan in The Legend of King Arthur (1979) and another as unit general manager Elizabeth Straker in the second season of Casualty (1987). She made numerous guest appearances in The Duchess of Duke Street ("Trouble and Strife"), Taggart ("Forbidden Fruit"), Cracker ("The Big Crunch"), A Touch of Frost ("Private Lives") and Heartbeat. She also appeared in an early episode of Jonathan Creek, playing Kirsten Holiday in the episode "Jack in the Box".

O'Brien was a member of the Everyman Theatre company.

In the 1970s she directed a production of Brecht's The Caucasian Chalk Circle at Ottawa University in Canada. 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.

O'Brien has also written seven detective novels: Close-Up on Death (1989), Deadly Reflection (1993), 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.