Born at Thorpe Malsor, Northamptonshire, Maunsell was the son of William Maunsell, Archdeacon of Kildare, and his wife Lucy, daughter of Philip Oliver. He married Caroline Elizabeth Cokayne, daughter of William Cokayne and Barbara née Hill in 1811 in London, and they had at least nine children: John Borlase; William Thomas (1812–1862); Lucy Diana (1814–1892); George Edmond (1816–1875); Thomas Cokayne (1818–1887); John Borlase (1820–1902); Sophia Caroline (1822–1889); Barbara Anna (1825–1842); and Charles Cullen (1827–1891).
