During his time in the Provisional IRA, Cahill helped import weapons and raise financial support.

[2] After his release, he continued to serve on the IRA Army Council and lead all financial dealings for Sinn Féin.

[3] Cahill was born above his father's small printing shop at 60 Divis Street on 19 May 1920[2] in West Belfast.

Soon after, he joined the Catholic Young Men's Society, which campaigned on social issues with a focus on eradicating moneylenders from working-class areas of Belfast, as they often charged usurious interest rates.

[2] At the age of seventeen, Cahill then joined Na Fianna Eireann, a republican-orientated Scouting movement.

The following year, 1938, at the age of 18, Cahill joined the local Clonard-based 'C' Company of the Belfast Brigade of the Irish Republican Army.

Tom Williams, the sixth IRA man to be charged, spent time in the Royal Victoria Hospital due to his injuries.

Cahill, Perry, Oliver, Cordner and Simpson, who had all been sentenced to life in prison, became free men in October 1949.

Joe and Annie were married on 2 April 1956 in St John's Church on the Falls Road in Belfast.

In the 1969 Northern Ireland riots, Cahill, along with Billy McKee, tried to defend the Catholic Clonard area from attack, but was unable to prevent Bombay Street being burned by Ulster Protestant rioters.

Angry at the failure of the IRA (led in Belfast by Billy McMillen) to defend Catholic areas during the communal rioting, Cahill and McKee stated in September 1969 that they would no longer be taking orders from the IRA leadership in Dublin, or from McMillen.

[6] In April 1971, after the arrest and imprisonment of Billy McKee, Cahill became the commander of the Provisional IRA Belfast Brigade.

Cahill authorised the beginning of the IRA's bombing campaign as well as attacks on British troops and the RUC.

To avoid the propaganda defeat that his capture would then have entailed, Cahill fled to the Republic of Ireland, temporarily relinquishing his command of the Belfast Brigade.

[2] In March 1972, Cahill was part of an IRA delegation that held direct talks with the British Labour Party leader Harold Wilson.

On March 29, 1973 he was arrested by the Irish Navy in Waterford, aboard the Claudia, a ship from Libya loaded with five tons of weapons.

Cahill stated at his trial that, "If I am guilty of any crime, it is that I did not succeed in getting the contents of the Claudia into the hands of the freedom fighters in this country".

However, in 1985, he spoke at the party's Ard Fheis in favour of republicans contesting elections and taking seats in the Dublin parliament, the Dáil.

[2] In his later years as honorary life vice-president of Sinn Féin, Cahill was a strong supporter of Gerry Adams and the Good Friday Agreement.

In 1994, a controversial but central aspect of the IRA's ceasefire was the granting of a limited visa by then United States President Bill Clinton to Cahill, in the face of opposition by John Major's government,[11] for the purpose of trying to win support for the new Sinn Féin peace strategy from Irish American IRA supporters.

In 1998 he stood in North Antrim in the elections to the Northern Ireland Assembly, but was unsuccessful, coming tenth with 4.07% of the people's votes.

He and several other former shipyard workers later sued the company for their exposure to the dangerous substances but only won minimal compensation.