I understand from the Deputy that the person in question has at least one Irish -born grandparent and so may make an application for citizenship through Foreign Births Registration.
Applications for citizenship via Foreign Births Registration are processed by the Department of Foreign Affairs and Trade. All applications and payments are made online and original documentation should be posted to the Department in support of an application. Detailed information on documentary requirements and how to apply is available on the Department's website at the following link www.dfa.ie/passports-citizenship/citizenship/born-abroad/born-abroad-citizenship-by-descent.
Alternatively, as the person concerned has also lived in Ireland for a number of years, he may apply to the Minister for Justice and Equality for Irish citizenship through Naturalisation. Relevant contact details are as follows:
Citizenship Division, Irish Naturalisation and Immigration Service, Department of Justice and Equality, Rosanna Road, Tipperary Town, E34 N566.