McKearney is raised in Moy, County Tyrone, Northern Ireland, in a staunchly Irish republican family. Both his grandfathers had fought in the Irish Republican Army during the Irish War of Independence, his maternal grandfather in south County Roscommon and his paternal grandfather in east County Tyrone. He is educated at local Catholic schools in Collegeland, County Armagh, and Moy, and later goes to St. Patrick’s Academy, Dungannon.
McKearney joins the Provisional IRA and is first arrested in 1972 on charges of blowing up the post office in Moy. He spends six weeks on remand, but is released due to insufficient evidence. In December 1973 he is arrested again and later sentenced to seven years for possession of a rifle. He is imprisoned in Long Kesh Detention Centre and later in Magilligan Prison. During this time, a younger brother, Seán, also an IRA paramilitary, is killed on May 13, 1974. He is released in 1977 but is sentenced to 14 years in August 1980 after being caught by the British Army with a loaded Sten gun along with fellow IRA member Gerard O’Callaghan. That same year an older brother, Tommy McKearney, who had been sentenced to life imprisonment for the murder of an off-duty Ulster Defence Regiment (UDR) soldier who worked as a postman in 1977, nearly dies on hunger strike after refusing food for 53 days. Another brother, Kevin, and an uncle, Jack McKearney, are both murdered by Loyalist paramilitaries in revenge attacks upon the family.
On September 25, 1983 McKearney takes part in the Maze Prison escape along with 37 other prisoners. At the beginning of 1984 he rejoins IRA activity in his native East Tyrone with the Provisional IRA East Tyrone Brigade. He advocates the commencement of the “third phase” of the armed struggle, the ‘strategic defensive,’ in which the Royal Ulster Constabulary (RUC), Ulster Defence Regiment and British Army would be denied all support in selected areas following repeated attacks on their bases. In 1985 Patrick Kelly becomes commander of the Provisional IRA East Tyrone Brigade and it is under his leadership that this strategy is pursued. Remote Royal Ulster Constabulary bases are attacked and destroyed, and building contractors who try to repair them are targeted and sometimes murdered, as occurs with the attack on the Ballygawley barracks in December 1985, which results in the death of two policemen, and The Birches police station in August 1986.
McKearney is shot dead by the British Army on May 8, 1987 during an IRA attack that he is taking part in upon Loughgall police station, which also claims the lives of seven other IRA members. His body is buried at his hometown of Moy.