Along with Dick McKee and Conor Clune, he was shot dead by his guards while under detention in Dublin Castle on the eve of Sunday, 21 November 1920, a day known as Bloody Sunday that also saw the killing of a network of British intelligence agents by the Squad unit of the Irish Republican Army and the killing of 14 people in Croke Park by the Royal Irish Constabulary.

[1] Educated at the local national school, which was close to his family home, at sixteen he became apprenticed in the drapery business of Dan Moloney, in Kildysart.

On completing his apprenticeship he went to Newcastle West, County Limerick, where he worked as an assistant in the drapery business of Michael O'Shaughnessy on Bridge Street.

[4] From there, he moved to Youghal, County Cork, where he lived at 6 North Main Street, from which address he wrote to his infant nephew in Chicago on 17 October 1912.

[1] Clancy was to distinguish himself in combat, when, with a group of Volunteers, he repelled an infantry attack at Church Street Bridge[7] and forced an enemy retreat towards the Phoenix Park on Easter Monday.

Shortly afterwards, Clancy personally burnt out a sniper from a house, and during the course of the Rising single-handedly captured Lord Dunsany and Colonel Lindsay.

[13] After his release from prison he was selected as the Sinn Féin candidate in the East Clare by-election, but his candidature was not ratified by IRA General Headquarters (GHQ) and Éamon de Valera was chosen at a second convention in Ennis.

[1] Clancy, in a letter to his brother M. J, who lived in Chicago, wrote about the divide in Irish society over the war and the split in the Volunteers, which he believed had resulted from the position adopted by John Redmond, the leader of the Irish Parliamentary Party: There is a very vast range of subjects on which I should like to write to you about; particularly with regard to the great European war.

[7]During the Irish War of Independence, Clancy became immersed in the underground movement and carried out a number of daring feats, which ensured his rise to become the second-in-command of the Dublin Brigade, IRA, with the rank of Vice-Brigadier.

[1] Clancy, along with chief of staff of the Volunteers Richard Mulcahy, was instrumental in the escape of leading Republican prisoners from Mountjoy Jail on 29 March 1919.

This unit was to function as an urban flying column, which was to specialise in the killing of British intelligence agents and those police who were attentive in combatting the IRA.

At its inaugural meeting the IRA leadership was represented by Peadar Clancy, along with Dick McKee, Michael Collins and Mick McDonnell.

On one occasion Peadar Clancy and Dan Breen waited for two hours outside the door of the practice of Dr. James Ashe, a specialist on Merrion Square whom French occasionally visited.

[9] The next morning, the Irish Independent published an article which described the attackers as "assassins" and included other such terms as "criminal folly", "outrage"' and "murder".

[16] On 12 February, Clancy again led a team of the Squad, this time in the attempted rescue of Robert Barton, who was to stand trial before a military tribunal.

[18] On 11 October 1920, Seán Treacy and Dan Breen narrowly escaped capture while staying in a safe house in Fernside, a middle class area of Dublin.

[19] On 14 October 1920, the Squad, along with Dick McKee and Peadar Clancy, planned to assassinate Hamar Greenwood, and General Tudor, two of the top British officers in Ireland.

Clancy was at Nelson's Pillar when he saw the trucks filled with soldiers pass, he surmised that the shop was to be raided, but had no way of warning his comrades.

The meeting was called to discuss the final arrangements for what would be the rout of the British secret service, with the elimination of the Cairo Gang.

[16] Clancy and McKee were also arrested in the early hours of the morning in another part of the city, though the Cairo Gang assassination plan was already in motion, for the next day.

It was later discovered they were betrayed to the British authorities by Irish former soldier James "Shanker" Ryan, variously described as "a ne’er do well", "a drunken bousey" and "a tout".

According to T. Ryle Dwyer, the room was being used as a kind of guardroom, and was furnished with some beds, tables and some stores, which included a box of hand grenades.

[16] According to Sean O'Mahony, they were tortured in the guardroom in order to extort from them the names of the Volunteers who had earlier that morning shot the fourteen members of the Cairo Gang.

[1] Robert Kee, in his work The Green Flag, writes, "though their bodies were riddled with bullets, their faces did not bear the marks of torture and brutality as has often been asserted.

Affidavits by MacLysaght and evidence given by both British and Republican members "give the lie to the false official version", according to Daniel McCarthy, as the article was published even before the military inquiry had reported its findings.

Its report, issued on 3 December 1920, found that death was the result of: "Bullet wounds fired by members of the Auxiliary Division, Royal Irish Constabulary, in self defence and in execution of their duty, i.e. in preventing the escape of the deceased party, who was in their lawful custody.

[3] It stretches credibility somewhat, according to Sean O'Mahony, that the garrison of Dublin Castle found it impossible to prevent the escape of three unarmed prisoners from the guardroom without shooting them.

Collins then went to their graveside, and was filmed stepping from the crowd to lay a wreath on the grave,[16] on which he pinned a farewell note, which read: "In memory of two good friends ― Dick and Peadar ― two of Ireland's best soldiers.

"[3] Later Collins, through his intelligence network, discovered the name of Corporal James 'Shankers' Ryan of the Royal Military Police, who was responsible for the arrest of the two Volunteers.

[26] Dan Breen, in his book My Fight for Irish Freedom, described both Clancy and McKee as "kindred spirits", who belonged to a small band of gunmen who would take any risk in the country's cause.