Post-Brexit, Northern Ireland (NI) would be a jurisdiction outside of an EU member state in the extraordinary circumstance where almost everyone who is born here will either be an EU citizen or entitled to be one.
This is because the UK expressly recognises in the Good Friday Agreement (GFA) that it is the birthright of the people of NI to choose Irish citizenship (or alternatively British citizenship or both). Under EU law, Irish citizens (or citizens of any other EU member state) are automatically also EU citizens. This does not change with Brexit.
The population of NI is around 1.8 million, while there are around three million other EU citizens in the UK. Irish citizens in NI retain some core EU citizens’ rights automatically, most notably rights to basic freedom of movement in the EU, in the same way any EU citizen in an existing third country (i.e. non-EU country) does. However, many subsidiary EU rights, opportunities and benefits would not be automatically retained on Brexit and would require a specific arrangement.
The December 2017 EU-UK Phase 1 Agreement (Joint Report) made broad commitments which would have ensured that Irish citizens residing in NI were able to continue to be able to ‘exercise’ and have ‘access to’ their EU rights, opportunities and benefits.
The Phase II negotiations were to examine the ‘arrangements required’ to do this – however this commitment has not been taken forward. There is no binding provision in the draft Withdrawal Agreement to implement this commitment, and the subject is not mentioned at all in the ‘Political Declaration’ on future arrangements.