Swanson initially trained as a classical ballerina at the Sadler's Wells Ballet School, before moving into musical theatre and film.

She had a strong support role in MGM's Knights of the Round Table (1953), and was the female lead in Hammer's film noir Third Party Risk (1954).

Swanson was signed to a long-term contract by the Rank Organisation, who put her in support roles in A Town Like Alice (1956) and Jacqueline (1956).

Initially titled Viscountess Ednam, she was styled as the Countess of Dudley on 26 December 1969, following her husband's succession to the earldom.

The Countess died on 16 November 2011 and was laid to rest in the private burial ground of the Earls of Dudley at the rear of the parish church at Himley.