This agreement was agreed by most of the people in Northern Ireland and the Republic of Ireland , as well as the Irish and British governments . As part of the United Kingdom , people from Northern Ireland are British citizens . They are also entitled to Irish citizenship by birth which is covered in the 1998 Belfast Agreement between the British and Irish governments , which , provides that : it is the birthright of all the people of Northern Ireland to identify themselves and be accepted as Irish or British , or both , as they may so choose , and accordingly ( the two governments ) confirm that their right to hold both British and Irish citizenship is accepted by both Governments and would not be affected by any future change in the status of Northern Ireland .