Killers' singer Brandon Flowers, Oscar-winning actor Tim Robbins and Paulo Nutini are among the artists who will be taking part in Arthur's Day today.
The celebrations, which mark the 251st anniversary of the opening of the Guinness brewery, will be centred around the Guinness Storehouse.
Snow Patrol will be the first band on stage after the toast at 17.59, 1759 being the year that the 9,000 year lease on the premises was granted.
They will be followed by the Manic Street Preachers, Biffy Clyro and Westlife in front of 2,000 fans in the grounds of the brewery.
Other bands taking part in the Dublin leg of the celebrations including Manic Street Preachers and local artists Westlife and The Script.
It will be a homecoming for The Script who currently have the number one album in Ireland and the UK. They grew up on James's Street where the brewery is located.
Later this evening Flowers and other major artists will play secret gigs in a number of pubs.
Sharon Corr and Imelda May are among the artists who will play in Cork and singer-songwriter David Gray and guitarist Newton Faulkner will play Galway.
In total there are 1,000 different events planned around the country.
All money raised from the concerts will go to a social entrepreneur fund setup by Guinness.
