PAYE in both Northern Ireland and Republic of Ireland...

I am currently living in the Republic of Ireland and working/paying tax in Northern Ireland.

What happens if I get a part-time job now in the Republic of Ireland to supplement my income. Do I:

1. Pay income tax as usual in Northern Ireland and pay income tax on my new job in the Republic of Ireland.
2. Pay both taxes through the UK tax system.
3. Pay both taxes through the Irish tax system.

Should you not be paying tax in ROI? The rates are lower in most instances anyway.

You have a double tax issue here.

The answer to your question is 1. for payroll taxes (Assume you are an employee). On employment income you (generally) pay taxes where work is carried out. Work in NI - pay UK payroll taxes, work in ROI - pay ROI payroll taxes.

However, as ROI resident you may well be liable to ROI tax on all income (including NI income) with foreign tax credit for UK tax paid.

This is a simple answer to a complex issue and you need to get tax advice.

I agree that you need some proper advice, but I am pretty sure that the only option allowable is option 1

Pay income tax as usual in Northern Ireland and pay income tax on my new job in the Republic of Ireland.

There is a joint tax agreement between UK / Ireland which clarifies how the tax authorities deal with your situation. There is a leaflet about it on
www.revenue.ie