James O'Mara (6 August 1873 – 21 November 1948) was an Irish businessman and politician who became a nationalist leader and key member of the revolutionary First Dáil. As an MP in the House of Commons of the United Kingdom, he introduced the bill which made Saint Patrick's Day a national holiday in Ireland in 1903. He was one of the few politicians to have served both as member in the House of Commons and in Dáil Éireann.
O'Mara was born in Limerick and educated by the Christian Brothers in Limerick, and at Clongowes Wood College in Dublin. His studies at the Royal University of Ireland were postponed after the death of his Uncle Jim in 1893, when James was sent to London to take over his Uncle's business functions. After his marriage in 1895 to Agnes Cashel, he moved to Epsom in Surrey, and then to Sydenham in London. He finally got his B.A. degree from the Royal University in 1898.
In the 1900 general election, O'Mara was elected unopposed as Irish Parliamentary Party MP for South Kilkenny.