During the ensuing Irish Civil War, MacSwiney supported the Anti-Treaty IRA and was imprisoned for it, resulting in her partaking in two hunger strikes herself.

[2] As Sinn Féin and hardline republicans became increasingly sidelined politically in the decade following the split, MacSwiney reacted by endorsing violence carried out by the IRA.

Towards the end of her life, she formally endorsed the World War II era leadership of the IRA under Seán Russell, who would go on to carry out the "S-Plan", a bombing campaign of Northern Ireland and England designed to weaken the UK in the face of Germany.

Born in London to an Irish father and English mother, she returned to Ireland with her family at the age of six and was educated at St Angela's School in Cork.

After receiving a loan from the Students' Aid Society in Ireland, she studied for a Teaching Diploma at the University of Cambridge,[4] which was normally reserved for men.

She worked at Hillside Convent, Farnborough, and considered becoming a nun, beginning a one-year noviciate with the Oblates of St Benedict, Ventnor.

[4] Influenced by her younger brother Terence MacSwiney's staunch Irish republicanism, she joined the Gaelic League and Inghinidhe na hÉireann.

[3] In 1917 MacSwiney was elected to the national executive of a newly reorganised Cumann na mBan, marking her increasing seniority amongst the women's side of the Republican movement.

[3] In the summer of 1920, a number of imprisoned Irish republicans went on hunger strike, most prominently the now Lord Mayor of Cork Terence MacSwiney.

[3] In the wake of Terance's death, Mary and Muriel MacSwiney embarked on a seven-month tour (1920–1921) of the United States, intended to raise awareness of the Irish cause in America.

The result was devastating to MacSwiney, and in the aftermath, she publicly endorsed threats of violence by the Irish Republican Army against pro-treaty TDs.

[3] MacSwiney was arrested at Nell Ryan's home (a safe house) in Ballsbridge on 4 November 1922 after it was raided by Free State soldiers.

Inactive Defunct In March 1926 Sinn Féin held its annual Ard Fheis, and the topic on the agenda was whether the party should accept the legitimacy of the Dáil and enter it.

De Valera proposed a motion to accept the Free State Constitution (contingent on the abolition of the Oath of Allegiance), but it was narrowly defeated by a vote of 223 to 218, with MacSwiney amongst those starkly opposed.

[3] At the June 1927 general election, MacSwiney lost her seat in the Dáil, as did every other remaining Sinn Féin TD, as their place as the primary republican party was completely eclipsed by Fianna Fáil.

[13] MacSwiney continued her efforts to reinvigorate the party but when Cumann na nGaedheal lost the 1932 election, she felt there was less need for the extreme oppositional position she had previously taken.

The entire incident pushed MacSwiney into pulling what little support she had been giving to Fianna Fáil and into backing violent militant republicanism.

When newly elected IRA Chief-of-Staff Seán Russell reached out to republican former members of the 2nd Dáil to help legitimise his position, MacSwiney responded and supported him.

[3] In 1923, Terence's widow Muriel left Ireland forever, dismayed that the Anti-Treaty IRA has lost the Irish Civil War.

[3] Upon learning of Máire's return to Ireland, Muriel engaged in a bitter legal battle with Mary that raged in the Irish courts.

Ultimately, an Irish judge would rule that Muriel's life in Europe was too chaotic for Máire, and that she should remain in Ireland with her aunt Mary.