The boy and his family, from Tipperary, were on holiday at the Quality Hotel in Redbarn, Youghal, County Cork.
The incident happened just before 14:00 local time on Monday. Lifeguards administered CPR before he was airlifted to Cork University Hospital.
The boy died on Tuesday after being transferred to the Children's University Hospital, Dublin.
A full investigation is under way into the incident.
A three-year-old boy has died after an incident at a hotel swimming pool in the Republic of Ireland.