The number of Monday to Friday 24-hour Tesco stores around the country is to increase from 12 to 27, with immediate effect.
In addition, the Tesco store at Wilton in Cork is to become the first supermarket in Ireland to open 24 hours a day, seven days a week.
The additional 15 stores are at Tallaght, Prussia St in Dublin, Greystones and Wicklow Town in Co Wicklow, Naas in Co Kildare, Youghal and Mallow in Co Cork, Ardkeen in Waterford, Ashbourne in Co Meath, Dundalk in Co Louth, Ennis in Co Clare, Castlebar in Mayo, Killarney Park in Kerry and Roscommon and Sligo.
Mr Dermot Breen, director of corporate affairs at Tesco, said the move was directed at customers who find it difficult to shop during traditional shopping hours.