Fenton was probably the daughter of a naval lieutenant named Beswick, but she bore the name of her mother's husband. She began as a street singer near her mother's coffeehouse in Charing Cross and made her debut in 1726 as Monimia in Thomas Otway's tragedy The Orphan; or, the Unhappy Marriage, in which she was an immediate success. She then joined the company of players under the management of John Rich at Lincoln's Inn Fields Theatre, London, where, on Jan. 29, 1728, Fenton became a sensation as Polly; a famous painting by William Hogarth shows her in one of The Beggar's Opera scenes. While at the peak of her career that year, she made her last appearance and ran away with Charles Paulet, 3rd Duke of Bolton, remaining his mistress until they married 23 years later.