The series chronologically covers the Troubles from its early beginnings emerging from the 1960s civil rights movement in Northern Ireland into the following three decades of armed conflict in the region between those fighting for a united Ireland and those fighting to remain part of the United Kingdom through to the Good Friday Agreement and beyond.

The Guardian wrote of how "by marking how the Troubles affected individuals, Once Upon a Time in Northern Ireland finds profound wider truths".

[2] The Daily Telegraph gave it five stars out of five, praising it as "a superb piece of work, not merely a litany of horrors but an opportunity for those involved to look back".

In the Los Angeles Times, Robert Lloyd praised how the series focused on how those interviewed "grapple with who they were then from the standpoint of who they are now".

[5] Reviewing the first episode for the Irish Examiner, Pat Fitzpatrick regarded it as "mesmerising", and the "narrative time-shifts" as elegant.