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.

[1] 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 returned to Dublin in 1914 to continue his work in the bacon business, and remained active in Sinn Féin.

He was elected as a Sinn Féin MP for his old constituency of Kilkenny South, defeating the Irish Party's Matthew Keating by 8,685 votes to 1,855.

A supporter of the 1921 Anglo-Irish Treaty, he was appointed as the first Irish Ambassador to the United States, but served only briefly.