Joseph Michael MacDonagh (18 May 1883 – 25 December 1922) was an Irish Sinn Féin politician. He was born in Cloughjordan, County Tipperary, the brother of the executed 1916 Easter Rising leader Thomas MacDonagh and film director John MacDonagh.
He was elected unopposed as a Sinn Féin MP for the Tipperary North constituency at the 1918 general election. In January 1919, Sinn Féin MPs refused to recognise the Parliament of the United Kingdom and instead assembled at the Mansion House in Dublin as a revolutionary parliament called Dáil Éireann, though MacDonagh did not attend as he was in prison. He was elected unopposed as a Sinn Féin Teachta Dála (TD) for the Tipperary Mid, North and South constituency at the 1921 elections. He also served as an alderman of Rathmines Urban District Council and Dublin Corporation between 1920 and 1922.
He was Director of the "Belfast Boycott", an attempt in 1920–21 to boycott goods from Ulster that were being imported into the south of Ireland. He opposed the Anglo-Irish Treaty and voted against it. He was re-elected for the same constituency at the 1922 general election, this time as an anti-Treaty Sinn Féin TD, but he did not take his seat in the Dáil. He died from the effects of a burst appendix on Christmas Day 1922.