Millions of revellers are due to raise pints of the world's most famous stout to toast the birth of Guinness.
A raft of global celebrations will mark Arthur's Day and 250 years since the Irish brewer went into business.
Dublin's St James's Gate will host the hub of festivities to commemorate founder Arthur Guinness and patrons will raise their glasses at 17.59 to celebrate the historical signing of its lease in 1759.
Tom Jones, Estelle, Kasabian, Natalie Imbruglia and former Destiny's Child band member Kelly Roland are some of the top names set to rock the Irish capital.
Model and socialite Jasmine Guinness, her father Patrick and siblings will be among the family members overseeing the celebrations at Guinness HQ.
But one of the eldest descendants of the famous brewer will be enjoying a more low key event at the site of the first brewery in Leixlip, Co Kildare. The Hon Desmond Guinness - the great, great, great, great grandson of Arthur - will be guest of honour at the town's Courtyard Hotel.
The 78-year-old said the worldwide celebrations were emotional, and joked he and his wife Penny will stay at the Courtyard until the Guinness runs out. "It's wonderful, it is very exciting," said Mr Guinness.
Cat Deeley and Boyzone's Ronan Keating will present the main concert at the Guinness Storehouse, which will be streamed live via Sky television to thousands of pubs throughout the UK on the day.
A host of artists will also perform at celebrations in 28 intimate pub venues across Dublin and in Lagos, Cameroon and Kuala Lumpur.
The Guinness brand, now owned by multinational drinks giant Diageo, is recognised around the world. The brewery was founded after Arthur Guinness secured a 9,000 year lease on the St James's Gate site for the annual sum of £45.
