Can an amanuensis become a master? David Dawson must surely be asking the question. For 20 years he worked for the ferociously singular (some might say appallingly solipsistic) figure who was fêted as our finest living painter, as the studio assistant of Lucian Freud. “Slave” was his nickname. It was jokily given yet, as with so many jokes, it was undercut by truth. The relationship was “hugely demanding”, Dawson says. “In my mind, Lucian always came first. And that was exacting. Sometimes I would think, ‘Just give me a break.’ ”

That break finally came when Freud died, aged 88, in 2011. Dawson, now 63, has, for the past 13 years, been free to follow his own course. So where has that led him? As the Lorcan O’Neill Gallery in Rome prepares to open a new exhibition of his paintings, Dawson reveals his true artistic self.

Some probably feel they already know Dawson — and often with an unsettling intimacy. How many people do you get to meet genitals first? Dawson has modeled for eight major Freud paintings. You may have met him sprawled nude, legs spread wide, his pet whippet, Eli, lolling sleepily beside him. You may know him from Freud’s final, unfinished work. Portrait of a Hound presents a hunched and naked assistant, his canine companion stretched languorously beside him. “Lucian kept pushing and pushing, even through the last weeks of his life, to get this painting into a state that he felt would be good enough to go out into the world. Eli’s ear is pricked and listening. And he is just catching you with a half-opened eye… That was the last detail that Lucian put on a painting. It was his very last touch.

Dawson stands alongside Freud’s portrait of him and his dog, David and Eli.

“Lucian knew me, or at least me as an adult, more intimately than anyone,” Dawson says. And in some ways, he ventures, he was equally close to Freud, “though relationships are all different”, he adds. “Lucian’s lovers would have seen aspects of him I never saw. The relationship that Lucian had with each of his sitters was theirs alone. He never put people together. I suppose he wanted to know each as an individual. But because I was around every day, I met everybody in the end.” Dawson’s address book — not to mention his social calendar — is certainly packed with an awful lot of rather well-known names.

From 1991 onwards, when Dawson first met Freud, the pair spent more time in each other’s presence than they did with anyone else. Dawson would habitually set off early every morning from the home where I first meet him in Kensal Rise, northwest London — an Edwardian semi-detached in a leafy cul-de-sac — to set up Freud’s studio in Kensington Church Street, central London, to which we progress. Typically, the two would breakfast together at Sally Clarke’s neighboring restaurant — coffee and pains aux raisins. They would go through the diary of a day that was divided into two working shifts. A morning session lasted from 8am until 1pm and was followed by a nap. Dawson would return to Kensal Rise at that point to paint himself. But he would frequently return in the evening to dine with Freud at the Ivy or the Wolseley where, one friend recalls, they would flick olives at any gawper who whisked out a surreptitious camera. Then Freud tended to return to his studio for a further painting session (often with one of his lovers) that would extend late into the night.

How many people do you get to meet genitals first?

Dawson was no mere sidekick. He was friend, confidant, adviser, fixer-upper and gofer all rolled into one. His job involved anything from standing off stage calmly handling a horse while Freud painted it, to donning the uniform of an absent Andrew Parker Bowles. It is his head that got plonked on the body of a nursing Jerry Hall after she twice failed to turn up for a sitting (“David’s left holding the baby,” Freud said with a laugh). It was Dawson who helped to decide which images should be destroyed, ripping into pieces those that didn’t make the grade so that pilferers couldn’t raid them from the dustbins as they did in the case of Francis Bacon.

Dawson took the impromptu photographs that now constitute a vivid record of Freud’s painting life. He snapped him as he worked on his portrait of Queen Elizabeth II (“I think it might be a little bit of history,” the Queen said). He caught the moment when Kate Moss, coming round bearing flowers for Freud, then close to death, climbed into his bed for a cuddle. “I’ve been keeping it warm for you,” the painter said as he pulled back the covers.

Lucien Freud with Kate Moss, in a photo taken by Dawson in 2010.

Dawson planted the garden that Freud’s studio windows overlook. He managed his diary, took his phone calls, banished moths from the basement or arranged for the car to be fixed. “He was maddening. Within half an hour of the Bentley having been gloriously polished, he would have gone through some bollards and scraped all the way down both sides.” He took Freud to his doctor, secured him the Solpadeine painkillers that he guzzled, stayed the night when he had panic attacks and once sneaked a woman to whom Freud had taken a sudden shine to the side of his hospital bed.

Little wonder that Dawson was floored by Freud’s death. “It felt like a train had hit me,” he exclaims. “For the first couple of years, I was just to-ing and fro-ing. It was raw grief. But, slowly, grief sinks down deeper and then you can live with it.”

Still, Freud left a strong legacy. Dawson has had to deal, since his death, with all sorts of administrative stuff. He is the director of the Lucian Freud Archive. He has curated a host of major posthumous exhibitions. He has co-authored a succession of books. His time has been entangled by a thriving Freud industry.

But he has now, at last, begun to distance himself. The Bridgeman Art Library is left to manage copyright issues — “No book covers, no images overwritten, no advertising… You would be surprised how many requests to advertise diet pills we have had,” Dawson says with a laugh. He hasn’t yet read the published outpourings of several Freud models and, though he remains on good terms with Freud’s complicated extended family (the artist had at least 14 children, although some reckon as many as 40, by several mothers, and 3 of his daughters were born in the same year), he gives a slight wince when I ask if he has tackled the most recent tome, a compulsively frank memoir by Freud’s daughter Rose Boyt. “I will get round to reading it one day,” he says.

Some of Freud’s sitters were left hurt and resentful, he admits. One moment he wanted them constantly with him but then, as soon as a painting was completed, they were dropped. “That might have felt tough, but it’s healthy,” Dawson insists. “What’s the point of a relationship that’s no longer real? There’s no room for people who are just hanging about. Freud put his painting first. He was working every day for bloody hours. That takes a lot of concentration and focus and energy. And besides, his important relationships always lasted. Caroline Blackwood [Freud’s second wife] spent the last four days of her life on the telephone talking to Lucian. And Freud was very generous to a lot of his models,” Dawson adds. “He handed out cars and flats like sweets.”

He bequeathed his own elegant Kensington townhouse to Dawson. And though the artworks that once adorned it, a Rodin bronze among them, were gifted to the nation, the walls are now hung with the plethora of Freud etchings that Dawson owns, among other pieces. Freud, a friend tells me, used to worry that he was far too demanding of his studio assistant, that he was stopping him from pursuing his own talent. Perhaps it is then fitting that, at the end, Freud should have left Dawson with the means to pursue his career without distraction, just as Dawson had for so long enabled him.

He caught the moment when Kate Moss, coming round bearing flowers for Freud, then close to death, climbed into his bed for a cuddle.

This sudden freedom proved daunting at first. While Dawson has moved into Freud’s former house, he has left the studio rooms untouched. Sheaves of brushes still lie on tabletops. Piles of old rags heap in corners. Accretions of crusty paint and scrawled aides-memoire adorn walls. Dawson occasionally works among them. He has done a few paintings of the studio that he may one day show. But for now he generally commutes back to his old Kensal Rise studio to work and, after what would appear to be a few false starts, he has finally found his true subject. Perhaps the greatest legacy of Freud was the lesson he offered Dawson on the fundamental importance to a painter of searching out his own truth. “This search is intoxicating,” Dawson declares.

It is something, he suggests, that he has always somehow known. Brought up on a remote moorland farm in Monmouthshire, the only son of a shepherd and his wife (he had one elder sister), he had a remote rural childhood. “Most farm boys love tractors and machinery,” he says, “but I always loved the animal husbandry best. I was good at it. I liked gathering in the sheep. Walking for eight hours a day with the dogs; standing waiting as someone else brings them forward. I noticed everything — how nature was interconnected, how I was a part of it. I learned to be comfortable with the facts of my solitary life.”

By the time he was 16, however, he wanted out. He had encountered a few of the hippies who in the Seventies had set up rural communities in Wales. Every year at shearing time — “A period that counted as party time in a quiet rural life” — he met New Zealanders from the other side of the world. “I realized that I wanted to see the world too, that it was imperative,” he says. By then, Dawson was coming to terms with his homosexuality. “I was beginning to feel that farming was going to be lonely, feeling an attraction to other men but not being able to act on it. That’s Dad’s life, I thought. I need to find my own life.”

Dawson had always been “quite good” at drawing, though he hadn’t had much time for it. He applied to art school and, with the encouragement of parents whom he describes as loving, affectionate and open-minded, he won a place first at Chelsea School of Art and then as a postgraduate at the Royal College of Art, where he shared a studio with Tracey Emin. You might have thought that his habitual reticence and her extrovert nature might have clashed. But they became close friends and on the day that I interview Dawson he has just returned from the opening of her latest show in Brussels. He doesn’t like to travel much any more, he says. “But you have to see your friends’ shows; you have to engage with what they are doing so that what you speak about with them remains properly real.”

By the time he was 21, Dawson faced a choice. “Dad said, you can’t have all this land and be an artist. You’ve got to do one job well, rather than spread yourself thinly.” The farm was sold. And David embarked on an artistic course. “But all the time I was in London, I felt that disconnect between my childhood and adult life. The two never quite joined.”

Then, 15 years ago, a farm came up for sale. Dawson was familiar with it. “It was on the other side of the hill from where we used to live: a very old-fashioned farm with a tenant farmer, which was perfect.” He bought it the next day without even bothering to go down and have a look.

Dawson in his studio, in Holland Park, London.

This farm and its life have become Dawson’s subject. The series of large canvases that will go on show in Rome were painted in large part en plein air in the hills. Dawson lugs an easel out into the fields and, regardless of the flies that blunder about in his pigments and the winds that threaten to blow away his canvases, he paints the sheep and the cattle in their pastures and sheds. He records the changing seasons, the rainbows and waterfalls, the race of the clouds across the sweep of the hills.

“I work in the land and with the land and the animals are around me and a part of it. I feel like I did when I was a boy, standing about waiting to herd the flock through a gate, except now I’m shepherding them into a painting.”

Dawson spends at least two weeks every month alone, painting on his farm in Wales. “I just slotted back in,” he says. “My neighbors remember me from school. They still call me Dai. Most have never heard of Lucian Freud, and if they have it doesn’t mean much. They’re more interested in the price of cattle or sheep.”

To him, that’s not boring. Quite the opposite. “I don’t want never to see anyone and to turn into a sort of bog person,” he says. “But I do think of how Lucian and his friends — Frank Auerbach, Michael Andrews, Francis Bacon — were always searching for something that felt fundamental. Something that somehow went beyond … not religious, but real. They were searching for a truth that they discovered through their own lived experience.” And that is precisely what Dawson, working on his farm in Wales, at last feels that he too has found.

“My life feels intact again. I am connecting back to the land, to my formative years, to my baseline and my roots. I feel like me reclaiming myself,” he says. “I’m confident in a quiet way that this is me painting myself.”

“Everything is autobiographical and everything is a portrait,” Freud said. Dawson believes that he is fully a part of the landscapes he paints. “For the first time in my life,” he says, “I feel like I am bringing my entire self to my work.”

Rachel Campbell-Johnston is the author of Mysterious Wisdom: The Life and Work of Samuel Palmer and the novel The Child’s Elephant