Sentimental Bloke sold 1000 copies a week in its first year. Families sent the special "trenches edition" to their men at war and soldiers passed around chapters torn from the book; one man got hold of 100 copies and sold them at inflated prices.

But by the time literary scholar Philip Butterss began work on the first full biography of Dennis, more than 12 years ago, his larrikin verse in books such as The Moods of Ginger Mick and The Glugs of Gosh had fallen out of fashion and the author had faded into the past.

So when Butterss received the $25,000 National Biography Award on Monday at the State Library of NSW, his book An Unsentimental Bloke was described as "long overdue" and "a forensic work of recovery" by historian Peter Cochrane from the judging panel.

In his "meticulously researched" biography, the judges wrote, "Butterss builds a portrait of the little boy whose strict and severe father was countered by adoring aunts, then the restless young man who became both a dandy and a larrikin." His story "illuminates the cultural ethos of the times as well as the character of a talented writer unable to change with those times".

A friend wrote a generous biography eight years after Dennis' death in 1938 and skirted around difficult aspects of his life such as his alcoholism and his political activism expressed in hard-hitting verse, some of it published in The Bulletin, and campaign work for the Labor Party.

"There was an understandable desire to see him as a sentimental bloke," said Butterss, who found a revealing stash of letters in the Angus and Robertson publishing archive at the Mitchell Library.

A sad letter from Dennis to his publisher, George Robertson, recorded his loss of the money made from his books through bad business decisions and over-spending. A letter from his wife to Robertson two years later admitted Dennis had been drinking heavily and asked the publisher to help by commissioning him to write another book, which he did.

Butterss, who teaches Australian film and literature at Adelaide University, did his PhD on Australian ballads at the University of Sydney and co-edited a book of ballads with Elizabeth Webby.

"Dennis was always a part of my life," he said. "He had a great ear for rhythm and wry humour." But his larrikin verse written in rhyming slang and his "embarrassing stage characters" represent an unfashionable kind of Australian masculinity.

In its 20th year, the Biography Award, founded with support from philanthropists Dr Geoffrey Cains and Michael Crouch, attracted 72 entries and has helped boost the quantity and quality of life writing.

Butterss won from a strong and varied shortlist: Moving Among Strangers: Randolph Stow and My Family by Gabrielle Carey, Citizen Emperor: Napoleon in Power 1799-1815 by Philip Dwyer, To Begin to Know: Walking in the Shadows of My Father by David Leser​, A Singular Vision: Harry Seidler by Helen O'Neill and The Feel-Good Hit of the Year: A Memoir by Liam Pieper.

Kim Williams will give the National Biography Award lecture on Wednesday evening at the State Library, speaking about biographies that have inspired him and his own memoir, Rules of Engagement.