O'Reilly, Myles William Patrick (1825–80), soldier and politician, was born 13 March 1825 in Dublin, only son of William O'Reilly (1792–1844) of Knock Abbey, Co. Louth, MP for Dundalk, and his wife and cousin Margaret Dowell O'Reilly. Myles was educated at St Cuthbert's College, Ushaw, Durham, and at the University of London, where he graduated BA (1845). He subsequently took the degree of LLD in Rome, where he established lifelong links with the catholic hierarchy. He was a captain in the Louth Rifles militia and led the life of a country gentleman on his Co. Louth estate, directing his own farming, breeding prize cattle, and riding to hounds. In 1860 he was invited by Pius IX to enter the pontifical service as commander of the St Patrick's battalion in the Irish brigade formed to defend the papal states. It was not an easy invitation for O'Reilly to accept, for he had only been married one year to Ida, daughter of Edward Jerningham of London, and the Irish brigade contained few members of his own class; however he was a catholic of great fervour and so proceeded to Italy where he was given the rank of major.
O'Reilly was only four months in Italy, most of which was spent in training the ill-equipped and ill-disciplined brigade, which had been without officers for months. He saw action only at the defence of Spoleto (17 September 1860), where he commanded seven different units of six nationalities speaking four different languages, and faced a force four times as strong as his own, better armed, and better trained. The Piedmonten–Sardinian army were confident they would take the city in two hours. In the event it took twelve hours, and the papal forces sustained remarkably few casualties and were able to surrender on favourable terms. O'Reilly's management of a difficult campaign was highly commended by his military seniors. On his return to Ireland he was feted and assured of a political future, being elected as liberal MP for Longford (1862–79).
In parliament O'Reilly was well regarded for his honesty and dignity; he sprang no surprises, having one clear agenda – the advancement of catholic interests. He was in constant correspondence with Archbishop Paul Cullen (qv) and was the voice of the church at Westminster. In 1862–3 he wrote two highly influential articles on education in the Dublin Review, asserting the denominational principle for Ireland and arguing that a charter should be granted to the Catholic University. With Charles O'Conor (qv), MP for Roscommon, he put the education question before parliament with unstinting regularity.
He was a tentative supporter of Isaac Butt (qv) and of home rule but stopped short of full commitment. He attacked Butt's 1876 land bill as subversive to property, and was accused by other MPs of being a mock home ruler. He was a JP for Louth and Dublin, and also found time to promote catholicism through scholarly writings. In 1868 he published Memorials of those who suffered for the catholic faith in Ireland in the 16th, 17th and 18th centuries. He vacated his seat in 1879 when he accepted the post of assistant commissioner of intermediate education in Ireland. He died in Dublin on 6 February 1880. He had four sons and two daughters.