Does a US citizen need an international license to hire car in Dublin Ireland?

Yes, in addition to a valid US driver's license, you will also need an International Driving Permit (IDP) to rent a car in Dublin, Ireland. The IDP is a translation of your US license into multiple languages and is required by law for all non-EU/EEA citizens driving in Ireland. You can obtain an IDP from your local AAA office or the American Automobile Touring Alliance (AATA).