A Dream Of Winter was published in a little-known magazine before Thomas would go on to become a household name.
But the 24-line poem lay forgotten in the archives until it was rediscovered purely by chance thanks to a university professor.
It will be given its first airing in decades at a “secret gig” in London - three days after what would have been the playwright’s 101st birthday.
And reading aloud the rare poem will be film star Celyn Jones - who won plaudits for his portrayal of Thomas in the hit film Set Fire To Our Stars alongside Elijah Wood.
Jones said: “It is quite incredible to think that after all these years a poem by one of the 20th century’s most famous writers had gone by unnoticed.
“When I got the call asking if I would do the honour and read it aloud, there was no way I could say no.
“It’s the literary equivalent of a lost Beatles track. It’s a beautiful poem and is full of the classic Dylan traits.”Swansea-born Dylan Thomas became one of Britain’s most loved writers - with his most famous works including Under Milk Wood and Do Not Go Gentle Into That Good Night.
Since his death in New York in 1953, his legacy has been cemented even further through several silver screen biopics, an international literary prize in his name and an annual festival.
So, it is perhaps not surprising that a lost poem of his has sent pulses racing among the arts world.
A Dream Of Winter features eight verses consisting of three lines and conjures up images of a birdless wood, soft snow and “singing statues”.
It was published in 1942 in British periodical Lilliput - which went out of business before the end of the Second World War. The magazine’s archives later came into the hands of late porn-baron Paul Raymond - who was blissfully unaware he had a lost Dylan Thomas classic in the vaults.
However, last year Swansea University professor John Goodby stumbled upon the work after being contacted by an old teacher from Marsh Hill Grammar in Birmingham.
Professor Goodby said: “I had dedicated one of my Dylan Thomas collections to a man called Peter Hellings, who taught me English and got me interested in Dylan Thomas in the first place.
“After his death, one of his colleagues Allan Wilcox was given a copy of his book, and inside was a ripped page from a very old magazine.
“Allan wrote to me saying he liked the book but could not understand why I had not included A Dream Of Winter in it.
“I had never come across the poem before - though there were fleeting references to it in some of Dylan’s letters.
“When I finally saw it I couldn’t believe it.”
After researching, Professor Goodby then traced the clipping back to Lilliput before finding an untouched copy of the magazine.
“It is completely fortunate the way this poem was found again,” he added. “If Allan had not have written to me then it could have gathered dust for another 70 years.
“It is amazing it went undiscovered for so long, but at the time it was published the poem would not been as significant as it is now.
“The poem was written around a series of photographs and they would have been more the priority back then. It’s worth noting that at this point Dylan did not really become a household name until 1946 when his radio programmes reached a mass audience.
“Also, given the poor quality of paper around the war it would have also made it more perishable.”
But what was initially regarded as a “throwaway” magazine article will now be given a proper premiere on Friday.
As well as having a star of the silver screen deliver Thomas’ lost words to an exclusive audience, the unveiling will also feature a painting inspired by the poem too.
Artist Dan Llywelyn Hall - who hit the headlines for his 2013 uncompromising portrait of the Queen - said: “Having worked from his words in the run up to the Dylan Thomas centenary, I often wondered what imagery would be whirling around his head as the poems are so intensely visual.
“When Prof Goodby invited me to make a piece to the painting it was a huge thrill to give a visualisation to these words that felt really resonated with me.”
And the man who will read aloud the poem admits to being excited and nervous in equal measure.
Jones, who has been writing a screenplay with comedy legend Eddie Izzard as well as working on a film about hoaxer Wearside Jack, said: “I’m really overjoyed. I still can’t believe it.
“To go from reading Dylan Thomas poems in school to starring in a film about him.....and then to be asked to read aloud one of his lost poems. It’s crazy - I’m trying not to over think it.
“But I’m sure it will be a night to remember.”