Jenny Tomasin's first major role came in the 1970s when she joined the cast of the London Weekend Television period drama Upstairs, Downstairs as Ruby, the kitchen maid to the Bellamy family. She appeared in the series from 1972, until it came to an end in 1975. She appeared in 41 episodes. Plans were made for a spin off series featuring Ruby, and fellow Upstairs, Downstairs characters Hudson and Mrs. Bridges, however, the series was never made, due to the death of Angela Baddeley, who portrayed Mrs. Bridges.
Tomasin's subsequent television appearances consisted mostly of discussion about her time in Upstairs, Downstairs, and her difficulties staying in the acting profession. "I feel the series might have limited me," said Tomasin, who was born on November 30 1936. "There are a lot of strong-woman parts I could have played, which nobody would see me as."
In 1985, Tomasin guest starred in the Doctor Who serial Revelation of the Daleks, the final episode before the series went on an 18-month hiatus, as the character Tasambeker. Tomasin held two roles in the soap opera Emmerdale. Between the years of 1981 and 1982 she portrayed the character Naomi Tolly, daughter of Enoch Tolly, who was killed in a tractor accident. Her second role was as Noreen Bell, a cantankerous villager who was killed off in July 2006.
Tomasin's role as Noreen Bell was her final role. On 19 January 2012, it was announced that the actress had died at the age of 75.