Forsyth’s television work includes Whatever Happened to the Likely Lads? as Thelma (1972–74); The Glamour Girls (1980-82) as Veronica Haslett; Tom, Dick and Harriet (1983) as Harriet Maddison; The Practice as Dr. Judith Vincent (1986); Sharon and Elsie as Elsie Beecroft (1984–85); Dark Season (1991) as Miss Maitland; and Boon (ITV, 1989) as Helen Yeldham. She has guested on The Bill; Doctor Who; Dr Finlay’s Casebook; Wycliffe; Agatha Christie’s Poirot; and also appeared in The Sinners; Holly as the title character Holly Elliot; Adam Smith; Bizarre and Rummage; The Master of Ballantrae; Jackanory; Holding The Fort; Waiting; Dangerfield; Running Wild; The Visit; Graham’s Gang; I Told You, Didn’t I?; Stanley’s Vision as Hilda Spencer; My World; Henry; Nice Town (1992) as Rosemary Dobson; Murder Most Horrid (BBC2, 1996, episode: “A Life Or Death Operation”) as Mrs. Osman; Spark (1997) as Mrs. Wells; and Playing the Field (BBC1, 1998) as Francine Pratt, and Heartbeat (2007). In March 1998, Forsyth made a guest appearance in Coronation Street as Ken Barlow’s dating agency client, Babs Fanshawe.

In 2002 Forsyth was the subject of This Is Your Life when she was surprised by Michael Aspel at BBC Broadcasting House. Forsyth appeared in the 2013 Christmas special of Still Open All Hours and returned for a full series on 26 December 2014 as Madge, sister of Maggie Ollerenshaw’s character Mavis.

Forsyth played the cello from the age of nine, but abandoned it once she went to drama school. Her ability was employed when, in 2004, she was cast in the lead role in Cello and the Nightingale, a play about internationally acclaimed cellist Beatrice Harrison that premiered at York Theatre Royal. She is now also playing cello in an all girl folk band called Becky & The Sharks.

In 2013 Forsyth appeared as Mrs. Jennings in Helen Edmundson’s BBC Radio 4 adaptation of Jane Austen’s Sense and Sensibility. Her stage work includes Calendar Girls in 2008 and Alan Bennett’s People in 2013. She had previously appeared in Bennett’s Single Spies in which she played the part of the Queen. In 2015 she appeared in Now This is Not the End at the Arcola Theatre in London.