Benjamin emigrated to the UK in 1960. Having left Rosemead Preparatory School to work in a bank, she studied for A-levels at night school. After a spell as a stage actress in West End musicals, she began presenting children's television programmes in 1976.

On stage, she has appeared in Hair, Jesus Christ Superstar, The Black Mikado, The husband in law and pantomime. On screen, she appeared in the 1975 horror film I Don't Want to Be Born and starred in the 1977 film Black Joy. On TV, her credits include Angels, Within These Walls, Crown Court, The Gentle Touch and Dixon of Dock Green. She appeared as Juniper in the first episode of Bergerac (1981).

She is chief executive of Floella Benjamin Productions, which has made television programmes since 1987.

In 2007, 2008 and 2009, she guest-starred in the Doctor Who spin-off The Sarah Jane Adventures as Professor Rivers from the Pharos Institute in the stories The Lost Boy, Day of the Clown and The Eternity Trap. She also narrated three "making-of" documentaries on the Doctor Who DVD boxset, The Black Guardian Trilogy.

In 2007, she played a minor role in the British comedy Run Fatboy Run.

Her 20th book, an autobiography Coming To England, was published in 1997.

She was awarded an OBE for services to broadcasting in 2001. At that time she was chairman of the British Academy of Film and Television Arts . She has also won a Special Lifetime Achievement award from BAFTA. She was chairman of the Women of the Year Lunch for five years and a Millennium Commissioner. She is president of the Elizabeth ’R’ Commonwealth Broadcasting Fund and a governor of the National Film and Television School. She was a governor of Dulwich College, where her mother once worked and her son attended. She is a Vice-President of the Royal Commonwealth Society.

In 2006, she became an honorary graduate of the University of Exeter and was awarded the degree of Hon D.Litt (Exon) for contributions to the life of the United Kingdom. She is styled Dr Floella Benjamin by the University on its website. She succeeded Lord Alexander of Weedon to become the Chancellor of the University of Exeter.

In 2008 she was appointed a Deputy Lieutenant of Greater London.

In the 2010 Dissolution Honours List announced on on 28 May 2010 she was appointed a Liberal Democrat Life Peer.

Her interest in education has also seen her on the "4Rs Commission" established by the Liberal Democrats to look into primary education in the UK.

She is vice-president of NCH Action for Children and Barnardo's, and was in the NSPCC’s Hall of Fame. She runs the London Marathon to raise funds for Barnardo's and the Sickle Cell Society. She is a cultural ambassador for the 2012 Summer Olympic Games.

In July 2007 she spoke of what she saw as the low standard of children's television. She features in the BBCs CBeebies animation Mama Mirabelle's Home Movies.