Marianne Wellesley, Marchioness Wellesley (née Caton, formerly Patterson; 1788 – 17 December 1853)^[1] was the American second wife of Richard Wellesley, 1st Marquess Wellesley, a brother of the Duke of Wellington.

She originated from Baltimore, Maryland, where her father, Richard Caton, was a merchant. The family was Roman Catholic, and Marianne's mother, Mary, was the daughter of Charles Carroll of Carrollton (died 1832), the last surviving signatory of the United States Declaration of Independence.^[2]

Marianne first married Robert Patterson, whose sister Elizabeth (died 1879) was the first wife of Jérôme Bonaparte, Napoleon's brother. The Pattersons (originally spelled Paterson) were wealthy neighbours of the Catons in Baltimore.^[3] The couple came to Europe for the benefit of Marianne's health,^[4] bringing with them two of Marianne's sisters. One sister, Louisa, married a baronet, Sir Felton Hervey-Bathurst, in 1813,^[5] and after his death married Francis D'Arcy-Osborne, later Duke of Leeds. Another Caton sister, Elizabeth, married George William Stafford-Jerningham, 8th Baron Stafford, as his second wife.^[6]