Dylan Thomas was born in the coastal town of Swansea, Wales. His father David, who was a writer and possessed a degree in English, brought his son up to speak English rather than Thomas's mother's native Welsh. He attended the boys-only Swansea Grammar School, (later known as Bishop Gore Grammar School, now reincarnated as Bishop Gore Comprehensive School), at which his father taught English Literature. It was in the school's magazine that the young Dylan saw his first poem published. Dylan Thomas's middle name, "Marlais", came from the bardic name of his uncle, the Unitarian minister, Gwilym Marles (whose real name was William Thomas). Thomas's childhood was spent largely in Swansea, with regular summer trips to visit his mother's family on their Carmarthen farm. These rural sojourns, and their contrast with the town life of Swansea, would inform much of his work, notably many short stories and radio essays and the poem "Fern Hill".

In 1937, Thomas married Caitlin Macnamara (1913-1994), and would have three children with her, throughout the relationship, littered with affairs. January of 1939 saw the birth of their first child, a boy whom they named (died in 2000). He was followed in March of 1943 by a daughter, Aeronwy. A second son and third child, , was born in July, 1949.

Thomas wrote half his poems and many short stories when he lived at 5 Cwmdonkin Drive—"And death shall have no dominion" is one of the best known works written at this address. By the time he left the family home in 1934 he was one of the most exciting young poets writing in the English language. He collapsed on November 4, 1953 at the White Horse Tavern after drinking heavily while in New York City on a promotional tour and later died at St Vincent's hospital. The primary cause of his death is recorded as pneumonia, with pressure on the brain and a fatty liver given as contributing factors. His penultimate words were: "I've had 18 straight whiskeys, I think this is a record." His final words were to Liz Reitell, to whom he said "I love you, but I am alone". Following his death, his was brought back to Wales for burial in the village churchyard at Laugharne, where he had enjoyed his happiest days. In 1994, his widow, Caitlin, was buried alongside him. Their former home, the Boat House, Laugharne, is now a memorial to Thomas.

Dylan Thomas is widely considered one of the greatest 20th century poets writing in English, frequently mentioned alongside Frost, Yeats, and T. S. Eliot in lists of the century's most important poets. He remains the leading figure in Anglo-Welsh literature. His vivid and often fantastic imagery was a rejection of the trends in 20th Century verse: while his contemporaries gradually altered their writing to serious topical verse (political and social concerns were often expressed), Thomas gave himself over to his passionately felt emotions, and his writing is often both intensely personal and fiercely lyrical. Thomas, in many ways, was more in alignment with the Romantics than he was with the poets of his era (Auden and Eliot, to name but two). Thomas' short stories are poetry exploded. Most notably is a semi-autobiographical selection published in 1940 entitled, 'Portrait of an Artist as a Young Dog', in which he explores his youth.

Thomas's circle, sometimes known as the "Kardomah Boys" after the coffee shop where they often met, included the composer and old school friend, Daniel Jones, the poet Vernon Watkins, and the artists Alfred Janes and Mervyn Levy.

He is particularly remembered for the remarkable radio-play , for his poem "Do not go gentle into that good night," which is generally interpreted as a plea to his dying father to hold onto life, and for the short stories "A Child's Christmas in Wales." and "The Outing". There are many memorials to Thomas in his home town of Swansea, including a statue in the maritime quarter, the Dylan Thomas Theatre, and the Dylan Thomas Centre. The latter building, formerly the Guildhall, was opened by ex-President of the United States Jimmy Carter, one of Thomas's most famous fans, following its conversion. It is now a literature centre, where exhibitions and lectures are held, and is the setting for the city's annual Dylan Thomas Festival.

Another monument to Thomas stands in Cwmdonkin Park, close to his birthplace at 5 Cwmdonkin Drive; this was one of his favourite childhood haunts. The memorial is inscribed with lines from one of his best-loved poems, "Fern Hill." Several of the pubs in Swansea also have associations with the poet. One of Swansea's oldest pubs, the .

It has been suggested that Bob Dylan, who was born Robert Allen Zimmerman, changed his name in tribute to Dylan Thomas. Bob Dylan has often denied this, responding in a 1966 interview, "Get that straight, I didn’t change my name in honor of Dylan Thomas. That’s just a story. I’ve done more for Dylan Thomas than he’s ever done for me." In 1965 he claimed that he took the name from an uncle named Dillon, adding, "I've read some of Dylan Thomas' stuff, and it's not the same as mine." In his 2004 biography, , however, Dylan admits that Dylan Thomas was relevant to his choice of alias (although he still acknowledges no influence or tribute, saying only that "Dylan" sounds like "Allen," his middle name and original choice for a surname de plume). Dylan is also billed as Robert Milkwood Thomas on Steve Goodman's "Some The crusted wound nor pat the brow; A hand rules pity as a hand rules heaven; Hands have no tears to flow"Dylan Thomas on Poets.org Biography, poems, audio clips, and related essays from the Academy of American Poets"The pub and the hellraiser: The poet, the actor, their pub, a furore" The Independent online edition 30 November 2005