Mary was the second daughter, and eventual sole heir, of Richard Bellings of Lanherne, Cornwall and his wife Anne Gage, daughter of Joseph Gage, of Sherborne, Oxfordshire. She married Henry, 7th Lord Arundell, in 1738, and they had one child, Henry. A portrait of Mary as an adult, attributed to Enoch Seeman, is in the collection of Oxburgh Hall, Norfolk (National Trust inv. no. 1210369).