After studying at the École des Beaux-Arts in Paris, Tessa Kennedy started her career in the 1960s at the London design firm of David Mlinaric, whose clients included Mick Jagger and Eric Clapton. In 1968, after spending three years working as partner with Mlinaric, she won a competition to design the Grosvenor House Hotel, launching her own company with Michael Sumner that same year. In 1986, she reformed as Tessa Kennedy Design, Ltd., a company which has won several design accolades. Her clients have included De Beers, Stanley Kubrick, George Harrison, King Husein of Jordan and London hotels Claridges, The Berkeley and The Ritz for which she was voted Designer of the Year.

A member of the British Interior Design Association (BIDA), Kennedy was the first woman to work in Saudi Arabia with her own company. Following two years as President of the International Society of Interior Designers in Britain and three years on the International Board, she made a Fellow of the International Interior Design Association (IIDA).