Proby was born at Bushey Park, Enniskerry, County Wicklow, the second son of Admiral Granville Leveson Proby, 3rd Earl of Carysfort, by Isabella Howard, daughter of the Honourable Hugh Howard.
Proby was born at Bushey Park, Enniskerry, County Wicklow, as the younger brother of Admiral Granville Leveson Proby, 3rd Earl of Carysfort, by Isabella Howard, daughter of the Honourable Hugh Howard.