Stagg is the seventh child in a family of thirteen children. He is born on October 4, 1942, in Hollymount, County Mayo. His brother, Emmet Stagg, is a Labour Party politician, formerly a Teachta Dála (TD) for Kildare North.
Stagg is educated to primary level at Newbrook Primary School and at CBS Ballinrobe to secondary level. After finishing his schooling, he works as an assistant gamekeeper with his uncle prior to emigrating to England in search of work.
Once in England he gains employment as a bus conductor in north London and later becomes a bus driver. Whilst in England he meets and marries fellow Mayo native, Bridie Armstrong from Carnacon. In 1972, he joins the Luton cumann of Sinn Féin and soon after becomes a volunteer in the Provisional Irish Republican Army (IRA).
In April 1973, Stagg is arrested with six others alleged to comprise an IRA unit planning bombing attacks in Coventry. He is tried at Birmingham Crown Court. The jury finds three of the seven not guilty. The remaining four are all found guilty of criminal damage and conspiracy to commit arson. Stagg and English-born priest, Father Patrick Fell, are found to be the unit’s commanding officers. Stagg is given a ten-year sentence and Fell twelve years. Thomas Gerald Rush is given seven years and Anthony Roland Lynch, who is also found guilty of possessing articles with intent to destroy property, namely nitric acid, balloons, wax, and sodium chlorate, is given ten years.
Stagg is initially sent to the top security Albany Prison on the Isle of Wight. In March 1974, having been moved to Parkhurst Prison, he and fellow Mayo man Michael Gaughan join a hunger strike begun by the sisters Marion Price and Dolours Price, Hugh Feeney, and Gerry Kelly.
Following the hunger strike that results in the death of Michael Gaughan, the Price sisters, Feeney, and Kelly are granted repatriation to Ireland. Stagg is denied repatriation and is transferred to Long Lartin Prison. During his time there he is subject to solitary confinement for refusing to do prison work and is also subjected, along with his wife and sisters during visits, to humiliating body searches. In protest against this he begins a second hunger strike that lasts for thirty-four days. This ends when the prison governor agrees to an end to the strip-searches on Stagg and his visitors. Stagg is bed-ridden for the rest of his incarceration in Long Lartin, due to a kidney complaint.
In 1975 Stagg is transferred to Wakefield Prison, where it is demanded that he again do prison work. He refuses and is placed in solitary confinement. On December 14, 1975, Stagg embarks on a hunger strike in Wakefield, along with a number of other republican prisoners, after being refused repatriation to Ireland during the IRA/British truce. Stagg’s demands are an end to solitary confinement, no prison work, and repatriation to prison in Ireland. The British government refuses to meet any of these demands. Stagg dies on February 12, 1976 after 62 days on hunger strike.
Frank Stagg’s burial causes considerable controversy in Ireland, with republicans and two of his brothers seeking to have Stagg buried in the republican plot in Ballina in accordance with his wishes, while his widow, his brother, Emmet Stagg, and the Irish government wish to have him buried in the family plot in the same cemetery and to avoid republican involvement in the funeral. As the republicans wait at Dublin Airport for the body, the Irish government orders the flight to be diverted to Shannon Airport.
His body is taken to Ballina and buried near the family plot. In order to prevent the body being disinterred and reburied by republicans, the grave is covered with concrete. In November 1976, a group of republicans tunnel under the concrete to recover the coffin under cover of darkness and rebury it in the republican plot.