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.

Another Caton sister, Elizabeth, married George Stafford-Jerningham, 8th Baron Stafford, as his second wife.

[7] Her family disapproved of the marriage because of Wellesley's reputation and his several children by his first wife, Hyacinthe-Gabrielle Roland.

[11] She died on 17 December 1853, aged 65, at Hampton Court Palace, and was buried at Costessey, Norfolk, home of her sister, Lady Stafford.