On 1 January 1957 he was second-in-command of the Pearse Column which carried out the raid on Brookeborough Royal Ulster Constabulary (RUC) Barracks in County Fermanagh, in which Seán South and Fergal O'Hanlon were killed.

[citation needed] In the October 1961 Irish general election, Ó Conaill ran as a Sinn Féin candidate in the Cork Borough constituency.

He was deeply involved in the drafting of the Éire Nua policy, working with Ruairí Ó Brádaigh, which was launched by Sinn Féin in June 1972.

On 20 June 1972, he represented the IRA along with Gerry Adams at secret talks at the home of Colonel Sir Michael McCorkell, Ballyarnett, County Londonderry.

The British representatives were Frank Steele, who presented himself as a government official but was an MI6 agent, and Philip John Woodfield of the Northern Ireland Office.

The meeting lasted four hours and the British side informed the IRA representatives that while Whitelaw refused to offer political status, he was prepared to suspend arrests of republicans and searches of homes.

On 7 July 1972 he was part of the IRA delegation which met with representatives of the British government in London (see article on Seán Mac Stiofáin for more details).

In September 1973, Hackett reported to Woodfield of the Northern Ireland Office that Ó Conaill was "losing ground to younger and more impatient operators.

"[11] In 1974, at a secret meeting arranged by journalist Kevin Myers, Ó Conaill and Brian Keenan had talks with Ulster Volunteer Force (UVF) leaders Billy Mitchell and Jim Hanna in Lough Sheelin, County Cavan.

In 1973, he gave the oration at the Easter Rising commemoration in Belfast, and the following year he spoke at the funeral of IRA hunger striker Michael Gaughan in Ballina.

He was found guilty of IRA membership and imprisoned in Portlaoise Prison, where in 1977 he was one of 20 men who took part in a 47-day hunger strike in protest at conditions in the jail.

Contrary to popular opinion, it was Ó Conaill and not Gerry Adams who proposed that Bobby Sands contest the Westminster by-election for Fermanagh and South Tyrone during the 1981 Irish Hunger Strike.

In 1983, along with Ruairí Ó Brádaigh, he resigned from the position of vice-president of Sinn Féin in opposition to the dropping of the Éire Nua policy.

He joined in the walk out led by Ó Brádaigh and was chairman of Republican Sinn Féin from 1986 to 1987 and subsequently a vice-president of the party.

Three days before his death he wrote a document entitled Towards a Peaceful Ireland, which offered a traditionalist republican solution to Irish partition.