The poet is described as "shy and retiring" in a previously unseen memoir written by the Thomas family's GP.
Prof John Goodby, of Swansea University, who discovered the documents, said they confirmed the poet's life in Wales "wasn't sensational".
"He was fairly modest, he was sober," said Prof Goodby.
The memoir belonged to Dr David Mendelssohn Hughes, Thomas' doctor in Laugharne, Carmarthenshire.
"He was respectful of the doctor and other authority figures and there was absolutely no womanising while he was living in Laugharne," said Prof Goodby.
"He had regular routines of visiting his mother and father every morning, doing the shopping, going to Brown's Hotel for a couple of pints and returning to the Boathouse to work for four hours or so."
While the memoir praises Thomas' character, it pours scorn on the behaviour of his wife, Caitlin, who is labelled a "first-class bitch".
Meanwhile, a letter written by Thomas to the landlord of a pub in Laugharne has also appeared for the first time.
Dated 8 November 1950, Thomas asks after the welfare of a pig he and the landlord were hoping to fatten up for Christmas. He writes that he is hoping for "a beautiful piggy Christmas" ahead of a trip to Persia in the new year.
The Doctor on Dylan Thomas
"The whole of the time that Dylan lives in Laugharne there has never been a breath of scandal involving Dylan with other women! With admiration of local females, married and unmarried, there surely existed opportunity for unfaithfulness but Dylan can be absolved absolutely from this.
"His capacity for drink was very limited compared with the average 'hearty'. He couldn't drink very much - three or four pints was his absolute limit - his daily limit was two pints in Brown's and on weekends with Phil in the Cross House. He never drank spirits, but in that last trip to America - described in that tragic book by John Brinnin - he undoubtedly posed as a hard drinking genius who could absorb whiskey and this cost him his life."
On Caitlin Thomas
"(Caitlin) is a nymphomaniac and a first-class bitch! What Dylan had to endure through her physical attraction and sexual prowess nobody knows - and I will not countenance any criticism of Dylan's shortcomings and beery excesses when they occurred without taking into account what he must have endured from Caitlin.
"On Xmas Eve after his death when his mother came to stay at the boat house for Xmas, she came home tight from the Browns with one of her local boyfriends - put on the gramophone and did a striptease in front of the children and Dylan's mother.
"I wonder did Dylan towards the end find life so heartbreaking that he deliberately went on drinking American whisky so as not to return??"
On Thomas' mother
"When his coffin came home from America and rested in his mother's house, no mother was prouder. I was glad that she lived to see him honoured by that magnificent performance of Under Milk Wood in Laugharne... But when the curtain dropped on that last performance on the Saturday night Dylan's mother died - just at that moment... She died rejoicing."
Caerphilly-born Dr Hughes - who died in London in 1981 - was based in St Clears and had met the Thomas family in 1938. He was Dylan's doctor until his death in 1953. He was also a keen oil painter and friends with Richard Burton.
He wrote the 26-page memoir at the request of the son of a family friend in the 1960s - a student at Cambridge.
It resurfaced after former Archbishop of Canterbury Dr Rowan Williams, whose love of Thomas' work started in school in Swansea, was told about it at a college reunion last year.
Prof Goodby said the memoir portrayed Thomas as "the victim" in his relationship with his wife.
"It says more negative things about Caitlin, who he sees as a disruptive force. He calls her 'fast' at one point - rather an old-fashioned word - but the mildest of the words he used about her.
"He sees her as one of Dylan's main problems and he surmises that this might be what pushed Dylan to indulge excessively when he went to America; that there was a kind of death wish there because of the collapse of his marriage to Caitlin.
"But elsewhere in the memoir what we get is the picture of a happy family man. A contented writer, somebody who was getting on with the business of writing the great poems that he produced at the end of his life."
Dr Hughes' memoir also details the death of Thomas' mother, Florence, in 1958 following a performance of her son's play Under Milk Wood.
It states she "died rejoicing" after the performance in Laugharne, which took place five years after her son's death in New York.
Prof Goodby said Thomas turned increasingly to alcohol during his visits to the USA, and the persistence of his notorious reputation was fuelled by the public's appetite.
"People don't want poets to be boring, it's as simple as that. They like their poets to be excessive and inspired by some kind of divine force. They want to see them acting out their own fantasies, perhaps being excessive on their behalf.
"It's comforting to see a poet, somebody who is a genius, have foibles and have failings like oneself."
Newly-discovered documents have cast doubt on Dylan Thomas' reputation as a hard-drinking womaniser.