Catherine Tate was born in Bloomsbury, London and brought up in the Brunswick Centre. Her mother, Josephine, was a florist and Tate has said that the character of Margaret in The Catherine Tate Show, who shrieks at the slightest of disturbances, is based largely on Josephine. Tate never knew her father, as he left very early on in her life, and consequently, she was brought up in a female-dominated environment, being cared for by her mother, grandmother and her godparents. By the time Catherine was a teenager, she knew she wanted to follow a professional acting career, and was sent to a boys' Catholic school at sixteen which had the necessary facilities for drama. Tate left school without sitting her A-Levels, believing that it was not necessary to have qualifications in order to study drama. She then tried for four years to get a place in the Central School of Speech and Drama, succeeding on her fourth attempt. She studied there for three years, and until the age of 26.

Tate began her television acting career with roles in serial dramas such as The Bill, and Casualty. She started stand-up comedy in 1996 and has appeared in comedy series such as The Harry Hill Show, Barking and That Peter Kay Thing. Soon after, she became involved with Lee Mack's Perrier Comedy Award-nominated New Bits show at the Edinburgh Film Festival in 2000. In 2001, she returned to the festival with her own sell-out one-woman show, which was followed by roles in Big Train, Attention Scum and TVGoHome. After being spotted at Edinburgh, she was given the role of Angela in the comedy, Wild West, with Dawn French, who commented "Catherine Tate is far too talented and she must be destroyed." Tate has also performed with the Royal Shakespeare Company, and at the National Theatre. She acted the role of Smeraldina in a 2000 RSC production of A Servant to Two Masters, and another role in The Way of the World at the National Theatre.

Tate was then given her own programme on BBC Two in 2004, which she co-wrote and starred in with Derren Litten, entitled The Catherine Tate Show, which ran for three series in all. Two of the show's well-known characters are teenager Lauren Cooper and Joannie "Nan" Taylor, the cockney grandmother. Tate's inspiration for the cockney grandmother came from visits to old people's homes when she was at drama college. Tate won a British Comedy Award for Best Comedy Newcomer for her work on the first series of The Catherine Tate Show. In November 2005, Tate appeared in another charity sketch as part of the BBC's annual Children in Need telethon. Tate later won a British Comedy Award for Best British Comedy Actress for her work in the second series of The Catherine Tate Show. At the end of 2005, she appeared in the BBC television adaptation of Bleak House.

The third series of The Catherine Tate Show aired in 2006, going on to win the National Television Award for most popular comedy as voted for by the public, and Tate's catchphrase "bovvered", used by her character Lauren Cooper, became so influential in popular culture that it was named Word of the Year and was even poised to enter the Oxford English Dictionary. Tate also played the role of Donna Noble in Doctor Who, a woman in a wedding dress who suddenly appears in the TARDIS at the end of the episode "Doomsday". The following episode, the Christmas special entitled "The Runaway Bride", saw Tate's character in a major role, where she was temporarily the Doctor's companion. Despite speculation that the third series of The Catherine Tate Show would be the last, Tate and the BBC have not ruled out further episodes. She later filmed a one-off special episode which aired on Christmas Day 2007.

She has been nominated for four BAFTA Awards for her work on The Catherine Tate Show to date, including Best Comedy Performance.