 Among his siblings were the Right Honourable Charles Arbuthnot and General Sir Thomas Arbuthnot.Arbuthnot was ordained a priest at Limerick on 2 November 1794, made vicar of Annaghdown and Killascobe in 1801 and rector of Crossboyne and Kilcoleman in 1808.He served as Archdeacon of Aghadoe (1809–1816) and Dean of Cloyne (1816–1823), before being elevated to the episcopy as Bishop of Killaloe and Kilfenora (1823–1828).