Background
The third of seven children, O'Leary was born in Dover, New Hampshire, to Michael and Margaret (née Howland) O'Leary.
The third of seven children, O'Leary was born in Dover, New Hampshire, to Michael and Margaret (née Howland) O'Leary.
He graduated from Mungret College in Limerick, Ireland in 1892, and then studied philosophy and theology at the Grand Seminary of Montreal in Quebec, Canada.
He was ordained to the priesthood by Bishop Maxime Decelles on December 18, 1897. He then served in parishes at Manchester (1898-1899) and Concord (1899-1904), and was named chancellor (1904) and later vicar general (1914) of the Diocese of Manchester. On June 16, 1921, O'Leary was appointed Bishop of Springfield by Pope Benedict XV. He received his episcopal consecration on the following September 8 from Archbishop Arthur Alfred Sinnott, with Bishops Michael Joseph Curley and George Albert Guertin serving as co-consecrators.
He aided the Russian War Relief following World War II. O'Leary later died at age 74.