He was the second surviving of three sons and two daughters born to William Monckton-Arundell, 2nd Viscount Galway and the former Elizabeth Villareal.

His father served as Receiver-General of the Crown rents for Yorkshire, Westmorland and Durham before being returned to Parliament as a Member for Pontefract and Thirsk.

[2] His maternal grandparents were Joseph Isaac Villareal and Kitty da Costa (a well known English Sephardi Jew who converted to Christianity; she was a daughter of Joseph da Costa, a gold and coral trader who owned Manor of Copped Hall in Totteridge).

[1] He was elected Member of Parliament to represent Pontefract from 1780 to 1783, made a Privy Counsellor in 1784 and knighted in the Order of the Bath in 1786.

Mary Bridget, the widow of Peter Auriol Hay Drummond (son of Archbishop Robert Hay Drummond and grandson of the 8th Earl of Kinnoull), was the only child and heiress of Pemberton Milnes of Bawtry Hall, Yorkshire (a prosperous wool-merchant from Wakefield) and Jane Slater (a daughter of Dr .Adam Slater).