Among the many accomplishments of the director Thomas M Wright’s riveting feature film debut, Acute Misfortune, is the rare sight of a real-life Australian journalist being portrayed on screen.

The film is an adaptation of Erik Jensen’s biography of the artist Adam Cullen, who the author – formerly a journalist for the Sydney Morning Herald, then the editor of the Saturday Paper, and now editor-in-chief of its publisher, Schwartz Media – was first assigned to write about when he was 19.

Wright and Jensen co-adapted the script, structuring it with two essential narrative trajectories. One points upwards, exploring the coming-of-age of the young and impressionable Jensen (played by Toby Wallace); and the other downwards, recreating the sad final chapter in Cullen’s alcohol-soaked and heroin-filled life.

Even rarer than watching an Australian journalist portrayed on screen is seeing them in a sex scene. In this case, a brief and tastefully staged bedroom moment between Jensen and his boyfriend. “I write sex scenes in all my stories. It’s subeditors who take them out,” Jensen jokes. “I’m happy that one is finally in there.”

The director Wright describes Cullen, who won an Archibald prize in 2000 for his portrait of David Wenham, as an “astonishing” artist whose early work contained “electric insights into the undercurrents of Australian culture.”

But Wright’s hauntingly poetic film is far from an idealised portrait, rejecting the idea that the greatness of the artist excuses the sins of the person.

“One of the disadvantages of many art biopics is that they’re films about genius,” Wright says. “So there is always this unknowable locus at the centre of the film, which is this person’s genius, that you can’t diagnose, and somehow implicitly seems to forgive them of some of their transgressions.

“Adam wasn’t a genius … He was a profoundly gifted painter. At some point in time, however, the train derailed. The paintings stopped working. His output was really uneven. Those insights he had so profoundly made metastasised into a fucking tumour. The very subject of his work started to look like a bad impression of the things he was discussing.”

Daniel Henshall gives a powerfully gloomy performance as the enigmatic, self-destructive artist tinkering on the precipice of oblivion. A very different picture of masculinity is drawn through the character of Jensen, who Cullen recruits to write his biography. Jensen describes himself back then as “a very ill-formed and ill at ease, unresolved person.” But he was also a dedicated writer, whose journalistic endeavours and obsession with his craft form a key part of the film.

“All I really had was my notepad. It produced in me a great sense of invincibility and also a huge sense of responsibility,” Jensen says. “I didn’t have a huge identity outside of the notepad. But when I was holding it, Adam could point a gun at me, and I wouldn’t even think to flinch. It felt like being a journalist gave me a licence to be somehow invincible. I don’t believe that any longer.”

The threat of a gun shot isn’t just a metaphor. Cullen’s behaviour was manipulative, and his lifestyle dangerous. He was constantly on drugs and fraternised with suspect characters including Mark “Chopper” Read, with whom he shared a close friendship (in fact, Wright says, Cullen was best man at Read’s wedding). He also had an obsession with guns: one time Cullen accidentally shot Jensen in the leg, and on another he was arrested for illegal possession of weapons. The painter regularly messed with the young writer, testing his loyalty and playing mind games. “He shot me to see if I would be scared off,” Jensen wrote for the Guardian in 2014. “When I wasn’t, he started to talk to me honestly.”

Despite the impressive final results, Acute Misfortune is the sort of book that tends to be described with that overused label of the “unfilmable novel”. It is structurally scrambled and unfolds as a series of fragments, with an elusive sense of time and place.

Jensen describes co-adapting it as a “rigorous and competitive” process, during which he “came to fully appreciate just how inflexible and unreasonable a person I can be”. The tension between himself and Wright, he says, created a film that is “better for it,” but “you would struggle to find a single line that we comfortably agreed on, at least first time around.”

Recounts Wright: “We both would fight tooth and nail. We actually had to get Christos Tsiolkas to come in at one point to mediate between us. There were certain matters on which neither of us would budge. We came to some interesting conclusions about how to handle this.

“It was profoundly personal for Erik, and profoundly traumatic terrain, as it was for many people who were close to Adam in his final years. There was a lot of trauma to unpack.”

Jensen has come to view the period of his life depicted in the film as “an extraordinarily large part of working out who I was as a writer and as a journalist, and as a person to some degree. But I don’t think I necessarily needed to submit myself to the trauma of that period to get through to being the journalist I am now ... I was driven by great, urgent, insecure ambitions and I found a subject who was willing to indulge and also exploit them.”

Did he come out of the experience a more cynical person?

“No. Cynicism is something that we cling to in journalism because it can be a shorthand for wisdom,” Jensen says. “If you’re cynical about things, you will more often unfortunately be right than you will be wrong. But for me in journalism, everything I do is another step away from cynicism. Increasingly I think of my journalism being born out of tenderness, and out of fragile ways of being.”

• Acute Misfortune is showing in Australian cinemas now