[4] His elder brother James was an early supporter of Sinn Féin, which Stephen also joined after the Easter Rising.
[1][5] In May, he went to the United States to replace his brother James as "fiscal agent" raising Dáil funds for the Irish Republic.
[5] In May 1922, O'Mara established a Limerick City Police Force to replace the withdrawn Royal Irish Constabulary.
[5] O'Mara was a loyal supporter of Éamon de Valera, who was staying at his home of Strand House the night the Treaty was signed.
[10] The evening before the 1922 general election, de Valera, O'Mara, and Boland dined together and discussed a possible grand coalition government.