Born in Reading, Berkshire, England, she took the stage name of Benjamin after her brother. Benjamin trained at the Redroofs Theatre School in Maidenhead. Her first acting role was as a child actress in Doctor Who in 1983 playing a young version of the character Nyssa. In 1989 she starred in the hit children's television programme Press Gang, where she played Julie Craig. She left after the first series for another role, but returned for the fourth and final series until 1993, where her role was expanded somewhat. In 1989 and 1990, Benjamin appeared in two series of LWT sitcom Close to Home, playing Paul Nicholas' teenage daughter Kate Shepherd. Also in 1990, Benjamin appeared in the BSB Galaxy Channel soap opera Jupiter Moon. In 1995 she appeared in the Adrian Edmondson and Rik Mayall comedy Bottom. However, she is best known for her role as Lisa Fowler in the BBC soap opera EastEnders which she played from 1998 to 2003 and was involved in several groundbreaking stories during her time there.
During her time on EastEnders, Benjamin was involved in one of the soap's most renowned and highly anticipated storylines, known as Who Shot Phil? (2001). The storyline centred around the shooting of her on-screen lover Phil Mitchell and who, out of the many potential candidates, actually performed the dastardly deed. Several suspects emerged and the audience was kept in the dark for many weeks as to the identity of the shooter. Benjamin's character was eventually unveiled as the shooter. However, despite her heavy involvement in the memorable plot, Benjamin was asked to leave the soap in 2002, as producers felt her character had run its course and there were no story options left for her. At the time she admitted that her axing from the show "gutted" her and "it felt like a punch to the stomach". She was asked back for a short period in 2003, however, to help with the forthcoming exit of Steve McFadden, who was taking a hiatus from the programme. Since leaving EastEnders, Benjamin has appeared in the BBC television programme The Afternoon Play, and the BBC hospital drama Casualty. She has also appeared in pantomimes across London as well as touring for 6 months in the play Framed in which she starred with Tom Craig from Coronation Street.
In April 2006 it was reported in the Daily Mirror that Benjamin is in talks with EastEnders about reprising the role of Lisa Fowler. Benjamin however has confirmed in a recent interview that all rumours of her returning to EastEnders were inaccurate and that the programme was not in contact with her. However, she did not rule out a return, saying "never say never". In June 2006, Benjamin appeared on The X Factor: Battle of the Stars, where she was the outright winner. She was mentored by the judge, Louis Walsh. She also appeared as Heather in Stephen Fry's drama Kingdom. In October 2006 Benjamin appeared in an episode of the BBC medical drama Doctors.
In September 2008 she appeared in All Star Family Fortunes winning £10,000 for her charity www.rosiesrainbowfund.co.uk She is currently starring in The Pretender Agenda, at the New Players Theatre (formerly the Players Theatre) with Lee Ryan. Benjamin stars also in the directorial debut from FX Artist Tristan Versluis the UK horror film called Not Alone. She was a contestant in the ITV1 series I'm a Celebrity…Get Me out of Here! (UK series 9) and was the first contestant voted out by the public on 23 November 2009.
Benjamin returned to EastEnders for a single episode on 5 August 2010 to facilate Barbara Windsor's departure storyline. In 2013 Benjamin will tour the UK Nationwide tour of the West End hit stage show, Hairspray.