Editing John A. Costello (section)

==Early life==
Costello was born on 20 June 1891, in [[Fairview, Dublin]]. He was the younger son of John Costello senior, a civil servant, and Rose Callaghan.<ref name=dib>{{cite web|url=https://www.dib.ie/biography/costello-john-aloysius-a2080|title=Costello, John Aloysius|work=[[Dictionary of Irish Biography]]|last=Lysaght|first=Charles|access-date=14 January 2023}}</ref> He was educated at [[St Joseph's, Fairview]] and then moved to [[O'Connell School]] for senior classes. He later attended [[University College Dublin]], where he graduated with a degree in modern languages and law. He studied at [[King's Inns]] to become a barrister, winning the Victoria Prize there in 1913 and 1914.

Costello was called to the [[Irish Bar]] in 1914 and practised as a barrister until 1922.<ref name=dib/>