Aloysius was born to John and Bridget O'Kelly in Peterson's Lane (now Lombard Street East), Dublin 3 July 1853.

The O'Kelly family along with Aloysius' cousins, the Lawlors, made up a network of artists and political activists in 19th-century Irish cultural history.

To enter the Gérôme's atelier was a great honour, however, the master was exceedingly strict and merciless in his criticism; such that a number of students could not last the distance.

In October 1881, Charles Stewart Parnell, a member of Parliament and leader of the Irish Party, was arrested and imprisoned in Kilmainham.

Two days following his arrest, Aloysius' brother, James J. O'Kelly, along with some other Party members, including John Dillon, were imprisoned where they remained until May 1882.