Motorists resident in Ireland with a UK driving licence are being advised to exchange that licence for an Irish driving licence in advance of a no-deal Brexit. My Department has always advised people to exchange their EU driving licence for an Irish driving licence once they become a resident of Ireland.
The Brexit Withdrawal Agreement provides for arrangements to recognise UK driving licences across the EU during the transition period, that is, until December 2020. In the case of a no-deal Brexit the UK will no longer be a Member State and so the UK driving licence will not be recognised. People resident in Ireland will no longer be able to drive on a UK, driving licence.
However, legislation in the Road Traffic Acts allows for the recognition of foreign driving licences for exchange purposes. If there is a no deal Brexit, the UK becomes a 3rd country and the potential then exists for arrangements to be made under this legislation. Ireland will be pursuing this option but cannot commence this work until the UK leaves the EU. This may take a little time to complete as it involves a formal agreement and legislation here in Ireland.