Northern Ireland's role as a Protestant entity has been eclipsed as the number of Catholics living in the UK enclave has exceeded the total of Protestants for the first time in the 2021 census.
The Northern Ireland Statistics and Research Agency said 45.7 per cent of respondents now identified as Catholic or were brought up Catholic, compared with 43.5 per cent identifying as Protestants.
A decade ago, the previous census showed Protestants outnumbered Catholics by 48 per cent to 45 per cent.
The proportion of people 10 years ago identifying as British was 40 per cent but the latest data showed that figure had slipped to 31.86 per cent, with 29.13 per cent identifying as only Irish. A share of 19.78 per cent identified as only Northern Irish.
The historic shift that some regard as likely to help drive support for the region to split from Britain and join a united Ireland comes only months after the 100th anniversary of the establishment of a separate government in Belfast after Dublin sought independence from the British empire.
A century ago, the Northern Ireland state was established with the aim of maintaining a pro-British, Protestant "unionist" majority as a counterweight to the newly independent, predominantly Catholic, Irish state to the south.
At that time, the population split was roughly two thirds Protestant to one third Catholic.
Northern Ireland's sectarian divisions can be traced back to the 17th century, when Protestant settlers from Scotland and England were "planted" in the north-eastern part of the island to bolster the authority of the English Crown. The alienation of the population in that region from Irish nationalist politics resulted in a decision in London to maintain sovereignty over the area when independence was granted.
The latest shift is likely to intensify calls for a referendum on reuniting Northern Ireland with the Republic of Ireland, as permitted under a 1998 peace deal that ended three decades of sectarian violence.
The data showed 46.64 per cent of the population hold only UK passports, 26.51 per cent only Irish passports and 5.49 per cent hold both — a number that has risen since the UK's Brexit referendum in 2016.
The census showed a 63.5 per cent increase in those holding an Irish passport, from 375,800 in 2011 to 614,300 in 2021.
Brexit will undoubtedly have been one factor in that surge, with people seeking an Irish passport to retain EU rights lost when the UK left the bloc.
The number of people holding a UK passport in Northern Ireland was one million in the latest census, down from 1.07 million in 2011.