Mary Norris was the daughter and eventual heir of Thomas Norris, MP, of Speke Hall, Lancashire, and his wife Magdalen Aston. She may have been born 22 March 1698 at Speke.
Her father died in June 1700 and left the Speke estates to his younger brothers, but gave his widow and daughter one third of the income each, though this caused a number of disputes and litigations. In 1730, or 1736, after the death of her uncles, Mary succeeded to the Speke estates.
She married on 9 December 1736, Lord Sidney Beauclerk, the fifth son of of Charles Beauclerk, 1st Duke of St Albans, and his wife Lady Diana de Vere. Lord Sidney was a notorious fortune-hunter
They had one son;
Topham Beauclerk, born 1739
Her husband died 23 November 1744, and Mary died 20 November 1766.