Born into a staunchly Irish republican, Roman Catholic family in Belfast, McGartland grew up in a council house in Moyard, Ballymurphy at the foot of the Black Mountain. His parents were separated and he had one brother, Joe, and two sisters, Elizabeth and Catherine. As the Troubles escalated, republican areas such as Ballymurphy increasingly came under the control of the local Provisional IRA (IRA) who, in the absence of normal policing, took on some policing functions. Their methods were not met with approval by all residents. One of the effects of the continuous rioting and the campaign of bombings and shootings in Belfast and all over Northern Ireland was to make McGartland grow up quickly.