The drink is produced at the St James's Gate Brewery in Dublin.
In 1914, when all of Ireland was part of Britain, it was the world's largest brewery, covering 64 acres.
Guinness is based on the porter style that originated in London in the early 18th century and is one of the most successful beer brands worldwide - and the best-selling alcoholic drink of all time in the Republic of Ireland, despite recent declining sales there.
Like Marmite, you either love Guinness or you hate it. Its burnt flavour is derived from the use of roasted barley.
Britain is the world's biggest consumer of Guinness, consuming at least 1 million pints of the black stuff a DAY, a tenth of all the Guinness drunk in the world daily. In 2007, Nigeria overtook Ireland as the world's second-biggest consumer.
Until the year 2000, more Guinness was sold in Britain and Ireland than the rest of the world put together.
And, if you are a fan of Guinness, you will probably know that Guinness isn't black, but dark red.
We celebrate 250 years of the Black Stuff as Guinness marks anniversary
By Sharon van Geuns
The Sunday Mirror
The Guinness brewery in Dublin
To a thirsty drinker, the 119.5 seconds it takes to pour a perfect pint of Guinness are sheer agony. And this year fans of the brew have been enjoying their favourite tipple for 250 years.
Founder Arthur Guinness signed a 9,000-year lease on his small Dublin brewery back in 1759.
Ten years later he exported his ale for the first time, when six-and-a-half barrels were shipped to England.
Britain is the world's largest consumer of Guinness, followed by Nigeria, which overtook Ireland into second place in 2007
Back then horse-drawn carts were the main source of transport to deliver the beer to pubs and move loads around the brewery. It’s said the horses received a ration of beer in their oats.
Arthur went on to become one of Ireland’s most successful businessmen and the founder of what became a worldwide phenomenon.
But what may surprise fans of “the black stuff” is that officially it isn’t black at all, but a dark shade of ruby red.
An advertisement, written in Irish, says "Is fearr de thú Guinness", which means "Guinness is good for you." Research has shown that Guinness may be good for the heart.
The colour comes from the way the barley is flaked and roasted. Its creamy white head is made up of nitrogen bubbles .
Every day, 10 million glasses of the brew are drunk and devotees include some unexpectedly famous names. Daniel Craig revealed he got into shape to play James Bond by drinking Guinness.
Ex-US President Bill Clinton and movie beauties Penelope Cruz and Gwyneth Paltrow are all partial to a drop.
Guinness is also famed for its publicity campaigns. The very first advert appeared in 1929, accompanied by the slogan which became advertising folklore: “Guinness is Good for You”.
The world's Top Ten biggest beer drinking nations (litres per person per year)
1) Czech Republic: 156.9
2) Republic of Ireland: 131.1
3) Germany: 115.8
4) Australia: 109.9
5) Austria: 108.3
6) Britain: 99.0
7) Belgium: 93.0
8 ) Denmark: 89.9
9) Finland: 85.0
10) Luxembourg: 84.4
The most iconic series of adverts was created in the 1930s and 1940s. Mainly drawn by acclaimed artist John Gilroy, they kept up the health angle with phrases like “Guinness for Strength”, “Guinness Makes You Strong” and “My Goodness My Guinness”.
The posters featured Gilroy’s distinctive artwork and more often than not featured animals such as kangaroos, ostriches, seals, lions and, most famously, a toucan.
The bird did, in fact, begin life as a pelican, but was changed by copywriter – and future thriller writer Dorothy L. Sayers – who realised “toucan” rhymed with more words.
The makers were told to stop hinting that the drink was a health tonic and the firm now makes no such claims. But many pregnant women like to sup the odd half-pint for its supposed iron-giving virtues.
In 1951, the company launched the famous Guinness Book of Records when Sir Hugh Beaver, the brewery manager, got into a disagreement about the fastest game bird in Europe while out hunting.
He couldn’t find the answer anywhere, so the idea for a book filled with the fastest, tallest and biggest things on Earth was conceived.
But when it comes to record-breaking drinks, the iconic brand of Guinness stands alone.
That’s why next month the company is holding a global day of celebration to mark the anniversary with live music and entertainment from big names like the Black Eyed Peas, Estelle and Kasabian.
After all, 250 years is worth raising a glass to...
Adapted from Guinness: Celebrating 250 Remarkable Years by Paul Hartley and Jane Birch. Published by Hamlyn on September 7, £9.99.