It is possible to drive in Ireland on a foreign licence for up to 12 months under the Geneva Convention, but this only applies to visitors. A person resident in Ireland must have an Irish or EU learner permit, or, a driving licence to drive here. Ireland cannot extend the validity of a driving licence issued by another licensing authority, nor can we unilaterally alter the provisions of an international convention.
As Ireland does not have a driving licence exchange agreement with the United States, there is no option but to go through the process of obtaining an Irish licence. Driver licensing law exists to ensure that people licensed to drive on our roads meet high standards of safety. The standards for testing drivers are set at EU level.
While a person who has a full but non-exchangeable licence will have to go through the normal driver learning process, they can avail of the shorter Essential Driver Training of 6 lessons instead of the usual 12, and they do not have to wait the usual minimum of 6 months before taking a driving test.