Duffett was born in Portsmouth, Hampshire. Prior to her soap roles, Duffett played the key role of Mrs. Bast in Ismail Merchant and James Ivory's 1992 film adaptation of Howards End. In 2008, she played Big Mo in the BBC film Dustbin Baby.
She remains best known for two long-running soap opera roles. After appearing as Debbie Bates in EastEnders from 1993 to 1995, she went into the role of boozy floozie Cat Matthews in Family Affairs. Cat first appeared in Family Affairs in late 1998, and was a key character in the show's story lines until the series ended in December 2005.
In 2016 she appeared in the BBC series The Coroner episode 2.4 "The Beast of Lighthaven" as Amy Penketh
