The daughter and sole heiress of Henry FitzAlan, 12th Earl of Arundel, she married Thomas Howard, 4th Duke of Norfolk.

On her mother's side, Mary was a niece of Henry Grey, Duke of Suffolk and first cousin of Lady Jane Grey, executed in 1554 after their alleged involvement in the Wyatt's Rebellion, which was intended to prevent the marriage of Queen Mary I with Philip II of Spain.

In 1556, her brother Henry, Lord Maltravers died, making Mary and Jane co-heiresses to the Earldom of Arundel.

[1] The marriage was arranged by the 3rd Duke of Norfolk, groom's grandfather in 1553-1554 with the aim of uniting the two most prominent Catholic families in England.

[7] However, according to Grummitt, 'The claims once made for her literary attainments have proved to be unfounded; the translations of classical texts surviving among the royal manuscripts in the British Library, once attributed to her, are children's exercises written by her stepdaughter Mary, later duchess of Norfolk'.