Monsell was born to William Monsell (1778–1822), of Tervoe, Clarina, County Limerick, and Olivia, daughter of Sir John Johnson-Walsh, 1st Baronet, of Ballykilcavan.
William Monsell (1778–1822) was the father of Monsell, who was born in Tervoe, Clarina, County Limerick, to William and Olivia, daughter of Sir John Johnson-Walsh, 1st Baronet, of Ballykilcavan.