Seán Mac Stíofáin (17 February 1928- 18 May 2001) was an Irish republican and first chief of staff of the Provisional IRA.

On July 25, 1953, Mac Stíofáin took part in an IRA arms raid on the Officers Training Corps School at Felstead in County Essex. In that raid, the IRA netted over one hundred and eight rifles, ten Bren and eight Sten guns, two mortars and dummy mortar bombs. The British police seized the van carrying the stolen weapons some hours later and on 19 August 1953, he was sentenced along with Cathal Goulding and Manus Canning, to eight years imprisonment by a court in Bishop's Stortford, Hertfordshire. In was in the run-up to the raid that Mac Stíofáin learned his first few words in Irish from Cathal Goulding. He later became fluent in the language, which he spoke with an English accent.

While incarcerated in Wormwood Scrubs and Brixton prisons, he learned not only a smattering of Greek from the Cypriot EOKA prisoners (he befriended Nikos Sampson) but also "the realities of an anti-British rule guerrilla campaign".[3]

Upon parole in 1959, Mac Stíofáin went to the Republic of Ireland with his wife and young family and settled in Dublin, and later Navan, County Meath, and became known under the Irish version of his name. Contrary to a number of accounts, this was not his first visit to the country and he had been to Ireland a month before the Felstead raid in 1953. He worked as a salesman for an Irish language organisation. He remained active in the IRA and gave the Bodenstown oration in 1959. A staunch and lifelong devoted Catholic, he distrusted the left-wing political direction – underway from 1964 – his erstwhile friend and IRA chief of staff, Cathal Goulding, was bringing the IRA. Appointed IRA Director of Intelligence in 1966, Mac Stíofáin was in a position to oppose the Goulding line and prepare the ground in the event of a split in the organisation.

In 1993, Mac Stíofáin suffered a stroke. On May 18, 2001, he died in Our Lady’s Hospital, Navan, County Meath, after a long illness at the age of 73. He is buried in St Mary's Cemetery, Navan.

Despite his controversial career in the IRA, many of his former comrades (and rivals) paid tribute to him after his death. Ruairí Ó Brádaigh, who attended the funeral, issued a glowing tribute, referring to Mac Stíofáin as an "outstanding IRA leader during a crucial period in Irish history" and as the "man for the job" as first Provisional IRA Chief of Staff. Gerry Adams and Martin McGuinness also attended. In her oration, Ita Ní Chionnaigh of Conradh na Gaeilge, whose flag draped the coffin, lambasted Mac Stíofáin’s "character assassination" by the "gutter press" and praised him as a man who had been "interested in the rights of men and women and people anywhere in the world who were oppressed, including Irish speakers in Ireland, who are also oppressed".