Does signalling give a driver priority when pulling out in Northern Ireland?

No. An indicator tells other road users what you intend to do; it does not give you priority or require them to make a gap.

Rules 103 and 159–163 of the Northern Ireland Highway Code make observation and safe manoeuvring essential. A driver emerging from a parking space or side road must check vehicles, cyclists and pedestrians before moving. Do not force another vehicle to brake sharply just because you have started indicating. Use mirrors, check blind spots and wait until your intended movement is safe.