The Irish have fought in many wars, and until 1922, mostly as part of the British Army. To locate records pre 1922 you will need to look at British service records.
The resources and weblinks on this page will be useful, however don't forget to use Google as part of your search strategy. There is more information being uploaded daily.
Also try our guide to English & Welsh Military Records to help locate information in the United Kingdom.
While you are in the Library don't forget to check out our databases:
Use Find My Past to locate: