C. J. Dennis spent his childhood in a succession of rural small towns in South Australia, and from 1890 to 1892 he was a boarder at Christian Brothers' College in Adelaide. After his mother's death, shortly before Dennis's fourteenth birthday, he and his two younger brothers were cared for by two unmarried aunts. According to Alec H. Chisholm, the celebration of the masculine, anti-authoritarian larrikin figure in Dennis's verse developed partly as a reaction to these aunts efforts to make sure the children were 'very well brought up'.
Dennis left school at the 17, working briefly as a clerk in Adelaide before going to live with his father at the Beetaloo Reservoir Hotel in Laura, a small town in the Flinders Ranges. In the late 1890s, Dennis had a stint as a journalist for the Adelaide weekly newspaper the Critic, but after about a year he returned to Laura where he assisted his father as a barman. Dennis's wife later wrote that Dennis claimed it was in these years that he 'learned to drink', a habit that would plague him for the rest of his life. After falling out with his father, Dennis travelled to the mining town of Broken Hill, working a number of odd jobs, before returning to Adelaide and rejoining the staff of the Critic.
From February 1906, Dennis teamed up with A. E. Martin to edit and publish the weekly newspaper the Gadfly. This paper was critically well received but commercially unsuccessful. At the end of 1907 Dennis left the struggling paper. After a brief period in Melbourne, he went to live in the isolated settlement of Toolangi, North-East of Melbourne, first camping with the artist Hal Waugh, and later renting a small shack. Here Dennis was able to concentrate on his writing. In 1908 his poem 'A Real Australian Austra-laise' was awarded a special prize in a competition run by the Bulletin, and in early 1913 Dennis produced his first volume of poetry, Backblock Ballads and Other Verses. It was not a success and Dennis continued to lead a marginal existence in Toolangi. However, a chance meeting with the educationalist R. H. Croll several years earlier had given Dennis an introduction to John Garibaldi ('Garry') Roberts, an official with the Melbourne Tramways Company, and his wife Roberta, enthusiastic patrons of literature and the arts. They owned a summer house, 'Sunnyside', in the Dandenong Ranges, where a group of artists and writers associated. The Roberts not only welcomed 'Den' (as his friends knew him) to their circle, but also provided him with a weekly allowance. Dennis divided his time between 'Sunnyside' and Toolangi until 1914 when he found work in Sydney with the union journals the Call and the Australian Worker. Dennis's hard-drinking lifestyle in Sydney could not be sustained, however, and he returned to Melbourne in September 1914, where the Roberts nursed him back to health. In early 1915, contacts in the Australian Labor Party secured Dennis a position as a clerk at the Navy Office in Melbourne, and the following year he became secretary to Senator E. J. Russell.
By this time Dennis's fortunes as a writer had dramatically improved. In Backblock Ballads and Other Verses, he included four interconnected 'verse tales' relating the story of a romance between a Melbourne larrikin and his sweetheart Doreen. The poems were narrated by the protagonist - dubbed 'The Sentimental Bloke' - which allowed Dennis to display his facility for vernacular verse in developing the slang idiom of 'the Bloke'. Dennis saw the popular potential of his love story. As early as October 1913, he had written to R. H. Croll that 'I have an idea that "The Sentimental Bloke" will go when published', and through 1914 Dennis expanded the series, submitting his 'Sentimental Bloke' poems to the Bulletin. In 1915, he managed to interest the Sydney firm of Angus and Robertson in publishing the poems as The Songs of a Sentimental Bloke. The mixture of a vernacular Australian narrative idiom with a sentimental love story clearly did appeal to a nation undergoing the strain of war. The book was wildly successful, and, as Chisholm observes, Dennis was transformed virtually overnight from 'a frayed little wanderer, battered by hard adventure in bush and city', to the most successful poet in Australia.
Dennis was quick to capitalise on his success. His next publication, The Moods of Ginger Mick, not only mined the same vernacular vein as The Songs of a Sentimental Bloke, it was set in the same imaginative universe: the title character, a former Melbourne larrikin turned heroic soldier, is a mate of Bill, the 'Sentimental Bloke', who again narrates the story. In 1917, Dennis followed it with Doreen, a slim volume of four poems centered on the domestic happiness of the now married 'Bloke'. Dennis expanded the world of 'the Bloke' again in 1918, with the publication of Digger Smith, about another soldier mate of 'the Bloke'. In the meantime, Dennis had also published the satire The Glugs of Gosh, and republished a revised version of his first book as Backblock Ballads and Later Verses. All these works featured the illustrations of Hal Gye, whose artwork provided an important complement to Dennis's verses. Dennis's his literary reputation as 'the laureate of the larrikin' stemmed from the The Songs of a Sentimental Bloke, which has remained enormously popular through most of the twentieth century.
Dennis used some of the proceeds of his publishing success to purchase land and an old wooden house at Toolangi, and in July 1917, married Olive Price, whom he had met through the artist David Low. He joined the staff of the Melbourne Herald in 1922 and his role as 'staff poet' occupied the bulk of his creative energies for the rest of his life; he produced a prodigious amount of 'copy' for the newspaper, writing verse and also prose pieces commenting on topical events. Dennis's last book, The Singing Garden, was based on his observations of the garden at his house 'Arden', at Toolangi. Dennis died of a heart condition brought on by asthma on 22 June 1938.
C. J. Dennis was chosen as one of 150 great South Australians by a panel of the Advertiser senior writers to celebrate the 150th Anniversay of the Advertiser newspaper, 12 April 2008.