She was born in Hammersmith, London, to Francis, a would-be poet, and Yvonne Macnamara. The couple had a son and three daughters; she was the youngest. The Macnamaras were descended from an old Irish land-owning family, and her grandfather, Henry Vee Macnamara, was the squire of two estates in County Clare. Francis moved in literary circles, being friendly with a number of artists, but when Caitlin was about four or five, he began to live apart from his family. Yvonne left London, and she and the girls settled in Ringwood, near New Forest, where they were close friends to Welsh artist Augustus John and his family. Macnamara was a precocious child, and was attracting male attention when only twelve years old. In her early teens she fell in love with Caspar John, son of Augustus John, despite the fact that he was almost eleven years her senior. During this period she had an affair with Augustus himself, who also painted her. In 1930, at the age of 16, she returned to London and entered a dancing school, and at 18 was a member of a London chorus line. She lived for a brief time in Paris before moving to County Clare in 1934, when her father returned to the Macnamaras' reduced estates.

Caitlin Macnamara was introduced to Dylan Thomas in a pub, either the Wheatsheaf or the Fitzroy, in Fitzrovia, London, in 1936 by Augustus John. She and Dylan bonded immediately, and that summer he travelled to Laugharne in Wales where Thomas and John were staying at the house of Richard Hughes. Dylan arrived with a friend, Fred Janes, and after the four travelled to Fishguard to view a painting exhibition, Dylan became drunk and jealous and started an argument with John. John punched Dylan and drove back to Laugharne with Macnamara. By the end of 1936, Macnamara and Dylan Thomas had begun a relationship through correspondence. By 21 April 1937 the couple were together in London and on 11 July 1937 they were married in Penzance, Cornwall. They had a peripatetic lifestyle, moving from Chelsea to Wales, then to Oxford, spending time in Ireland and Italy before returning to Oxfordshire. They eventually settled in a rented cottage in Laugharne in the spring of 1938, before moving into the 'Sea View' a couple of months later. In 1949 the house which would become the Thomas' family home, the Boat House, came on the market for £3000, and was purchased by Margaret Taylor, wife of historian A. J. P. Taylor, one of Dylan's benefactors. Caitlin Thomas had three children by Dylan, Llewelyn Edouard (1939-2000), Aeronwy Thomas-Ellis (1943-2009) and Colm Garan Hart (born 1949).

Although Dylan tried to portray himself as a bohemian character, it was Caitlin who was the true rebel. Vera Philips, a childhood friend of Dylan's from Swansea, recalled Dylan had the proper Welsh background, ... He was brought up like me, worrying "What will the neighbours think?" Whereas Caitlin didn't care a bugger what anyone thought.

Their marriage was a notoriously stormy affair, fuelled by alcohol and infidelity. Thomas once famously described their relationship as "raw, red bleeding meat". Despite their fiery marriage, she jealously protected both Dylan and his reputation, and tried to protect him from others and himself. Although Thomas was known for her belligerent personality, some writers have shown sympathy for a woman who was at the receiving end of Dylan's sometimes foul-mouthed abuse and pouting silences. Thomas became more and more resentful of her role as a stay-at-home mother, compounded by the run-down nature of their home, the Boat House, which had neither electricity nor running water.

The relationship between the couple deteriorated further when in 1950, Dylan undertook the first of his tours of America. The trips were arranged as a lucrative venture to gain capital to fund Dylan's poetry writing while back in Britain, though by the time of his return, the money he had accumulated did little more than repay outstanding debts. Furthermore, Thomas had become more and more frustrated at being left behind, dealing with the children and the bills, while her husband spent his time carousing in another country.

In 1953, Dylan travelled to New York without her, undertaking recitals of his poetry to American audiences. On 5 November Dylan collapsed with breathing difficulties and was admitted to hospital. Caitlin travelled to America to be with her husband, though her reaction on arriving at his death bed was aggressive, reportedly shouting "Is the bloody man dead yet?". In Thomas' autobiography, Caitlin: Life with Dylan Thomas, she states that she had no recollection of using the words, but she was, by her own words, "stinkin drunk" by the time she arrived. Other reports state that when Thomas found another woman tending to her comatose husband, she flew into a fit of rage, biting an attendant and fighting with bystanders until she was subdued.

In 1957 Thomas published a frank account of her later life and reflections on her life with Dylan, titled Leftover Life to Kill, though she refused to collaborate with most of her husband's biographers in later years. In a memoir published in 1982, she described her relationship with Dylan as "Predominantly a drink story because without the first-aid of drink it could never have got onto its rocking feet." Although their relationship was tempestuous, writings in a personal journal uncovered over fifty years after Dylan's death showed Thomas' passion and love for her husband.

After Dylan's death in 1953, Thomas returned to Laugharne, but she was desperate to leave the village, referring to it as a "permanently festering wound". Thomas spent less and less time in Wales, and made several journeys to Ireland and Italy. She spent an increasing amount of time in Italy, staying on Procida, until, in 1957, she decided to relocate to the country. She left Britain with her children in September of 1957, and moved to Rome with a Welsh actor and writer, Cliff Gordon. Gordon was homosexual, and his main purpose in Rome appears to have been as a drinking partner for Thomas. Towards the end of 1957, while eating at a restaurant on Via Margutta she met Giuseppe Fazio, a Sicilian 'director's assistant'. The couple began a relationship soon after, which lasted until Thomas' death. Although they never married, they had a son together, Francesco, who was born on 29 March 1963 when Thomas was 49. In 1963, while in Italy, she wrote her second book, Not Quite Posthumous Letters to My Daughter.

By her own account, after the death of Thomas she experienced severe emotional and psychological distress, and was treated in clinics and asylums in London, Rome and Catania. She began to attend Alcoholics Anonymous in 1973, aged 60. In 1982 she and Fazio left Rome and moved to Catania, Sicily, eventually moving into a house left by Fazio's mother.

Caitlin Thomas died in Catania on 31 July 1994 following a long illness, aged 80. She was buried next to Dylan in Laugharne, though the burial request came as a surprise to her family, with her daughter believing that she would have preferred to have been buried in Italy after spending so much of her later life there.

In 2008 a film portraying Thomas' life with Dylan was released. The Edge of Love, previously known by its working title The Best Time of Our Lives, saw Thomas played by Sienna Miller in a story that reflects the relationship between Thomas and Vera Philips, Dylan's childhood friend. A second movie, Caitlin, with Miranda Richardson and Rosamund Pike depicting the title character at different points in her life, was to be produced the same year, but failed to reach the screen.

The Australian rock band The Paradise Motel named their 1997 debut album after the title of Macnamara's autobiography.

Caitlin MacNamaraCaitlin MacNamara