To find records of his birth do you have an estimated birth year? Civil registration began in Ireland in 1864 so all birth registration from that time up until 1918 are available to view for free online at https://www.irishgenealogy.ie
. However, if your ancestor was born before that time (as I presume is more likely) you would have to rely on parish records. Do you have any idea what part of Ireland he came from? Parish registers are available to view for free online also but can be tedious to search through and you would want to know a general area where he may have come from to search them.
With a little more information I might be able to help you more.
Hoping I can help,
The Genealogy Geniehttps://thegenealogygenie.com