The rule for a US licence
Ireland does not require an International Driving Permit from visitors holding a license issued in English. The US Embassy states that US citizens may drive on their US license for a tourist visit of up to 12 months.
An IDP is only relevant if your license is in a language other than English, in which case a translation or IDP is expected.
Live in Ireland, or hold an EU/EEA licence?
A licence issued in Ireland is what you drive on at home - an IDP is a translation of a foreign licence, so it does not apply to you here. An EU or EEA licence from another member state is also valid in Ireland on its own, under EU Directive 2006/126/EC. In neither case do you need an IDP.
At the rental counter
Irish rental agencies focus on license validity, age, and endorsement history rather than an IDP. Note that many Irish rentals are manual transmission, and automatic vehicles need booking well in advance.
What the permit covers
An International Driving Permit is a translation of your licence into a standard multilingual booklet, issued under the 1949 and 1968 road traffic conventions. It is not a licence, and it is never valid on its own: you carry it with your own licence, and police expect to see both.
It is issued against the vehicle classes already on your home licence, and it never adds one. If your licence does not cover motorcycles, an IDP does not let you ride a scooter in Ireland; if it does not cover a heavier vehicle, the permit will not cover a camper or a minibus either. The permit restates what you already hold, in a form the local authorities can read.
Driving in more than one country?
Check every destination on your trip at once - Ireland is already filled in.
Check your tripOther destinations
Informational only, not legal advice. Requirements change and vary by length of stay, rental company, and vehicle class. Always confirm with the destination's embassy or your automobile association before you drive.