Eamonn S. or Edmund J. Duggan (Irish: Éamon Ó Dúgáin; 1874 – 6 June 1936) was an Irish lawyer, nationalist and politician, a member of Sinn Féin and then Cumann na nGaedheal.
Born in Longwood, County Meath, Duggan's father was a Royal Irish Constabulary officer from County Armagh serving in the village, his mother a local woman by the name of Dunne. Duggan qualified as a solicitor and soon became involved in politics. He became a supporter of Sinn Féin and fought in the Easter Rising in 1916. He was subject to court-martial following the Rising and sentenced to three years penal servitude. Duggan was released in 1917 under general amnesty and went back to practicing law. For a time he also served as Irish Republican Army Director of Intelligence.
Duggan was elected to the First Dáil Éireann for South Meath in 1918. At the end of 1920 he was re-arrested and not released until the end of the Irish War for Independence in July, 1921. After the Truce he was appointed chief liaison officer for the Irish government. In October 1921 Duggan was appointed as one of the five envoys to negotiate and conclude a treaty with the British government. He signed the Anglo-Irish Treaty at 22 Hans Place, London.
In the post-Treaty provisional government he was appointed Minister for Home Affairs and later became parliamentary secretary to the Minister for Defence and to the Executive Council. He declined to go forward in the 1933 general election but was elected to Seanad Éireann.