Seán Mac Diarmada, also known as Seán MacDermott, was an Irish republican political activist and revolutionary leader. He was one of the seven leaders of the Easter Rising of 1916, which he helped to organise as a member of the Military Committee of the Irish Republican Brotherhood (IRB) and was the second signatory of the Proclamation of the Irish Republic. He was executed for his part in the Rising at age 33.

The Easter Rising, also known as the Easter Rebellion, was an armed insurrection in Ireland during Easter Week in April 1916. The Rising was launched by Irish republicans against British rule in Ireland with the aim of establishing an independent Irish Republic while the United Kingdom was fighting the First World War. It was the most significant uprising in Ireland since the rebellion of 1798 and the first armed conflict of the Irish revolutionary period. Sixteen of the Rising's leaders were executed starting in May 1916. The nature of the executions, and subsequent political developments, ultimately contributed to an increase in popular support for Irish independence.