He succeeded his father in 1744 to estates in near Tandragee in county Armagh; near Lough Gur in county Limerick; at Basildon House in Berkshire; and near Tiverton in Devon.
William Sampson Guy's grandfather was Thomas Guy, Sr. (1812 – December 18, 1883), who was born in Tanderagee, County Armagh, Ulster, Ireland.