C. J. Dennis was born in Auburn, South Australia. His father owned a hotel in Laura, and his mother suffered ill health, so Clarrie (as he was known) was raised initially by his great-aunts, then went away to school, Christian Brothers College, Adelaide as a teenager.
At the age of 19 he was employed as a solicitor's clerk. It was while he was working in this job that, like banker's clerk Banjo Paterson before him, his first poem was published. He later went on to publish in The Bulletin, as Paterson and Henry Lawson had also done. The three are often considered Australia's three most famous poets; though Dennis's work is less well known today, his 1916 publication of The Sentimental Bloke sold 65,000 copies in its first year, and by 1917 he was the most prosperous poet in Australian history.
The Songs of a Sentimental Bloke and numerous spin-offs published subsequently related the everyday adventures of the title character (name unknown), his girl Doreen, his friend Ginger Mick, and other characters. The poems are written in dialect, and present the Sentimental Bloke as a typical larrikin.
The Sentimental Bloke was adapted as a stage play, a silent film of the same name, a sound film, and a musical over the following decades. In 1983, Australia Post featured the Sentimental Bloke on a series of stamps. A poetry prize named in Dennis's honour is presented regularly by the Premier of Victoria.
Shorter works were also published in a wide variety of Australian newspapers and magazines.