The East Tyrone Brigade, Briogaid Tír Eoghain Thoir, of the Provisional Irish Republican Army (IRA) was one of the most active republican paramilitary groups in Northern Ireland over the course of the Troubles. They are believed to have drawn their membership from right across the eastern side of County Tyrone as well as north County Monaghan and south County Londonderry.

The east of the county has a long history of militant Republicanism from Tom Clarke, Joseph McGarrity, Liam Kelly, Gerry McGeough, Tommy McKearney, Bernadette Devlin McAliskey and Martin Hurson. The IRA's heaviest single loss of life since the 1920s involved the East Tyrone Brigade, where a group of eight volunteers were ambushed and killed by the British special forces, the Special Air Service (SAS), during an attack on the Royal Ulster Constabulary (RUC) station at Loughgall on 8 May 1987.