The eldest son of Irish migrants, Bernard O'Dowd was educated at state schools, against his parents' Catholic convictions, to make him eligible for educational scholarships. In the 1880s he worked briefly as a teacher in a Catholic school, but was discharged for heresy. In 1886, after passing the Public Service entrance examination, he moved to Melbourne, beginning his long career with the Victorian government. Over the next forty years O'Dowd worked in several positions, eventually becoming Chief Parliamentary Draughtsman for Victoria. His rise through the ranks of the Public Service was assisted by degrees in arts and law that he acquired during the 1890s.
In 1882 O'Dowd's first poems were published in the Ballarat Evening Post. His membership in many Melbourne clubs helped to stimulate his thinking. A period of correspondence with the American poet Walt Whitman convinced him of the value of poetry for the improvement of society, ideas that he elaborated in his famous "Poetry Militant" address in 1909. He was joint-editor of the radical weekly, Tocsin, and eventually produced a regular column, often participating in the federation debate. His first book of poetry, Dawnward?, was published in 1903, containing the often anthologised poem, "Australia". Several more volumes appeared in the next decades, but O'Dowd's best-known volume is The Bush (1912) in which he presented what many critics regard as one of the most significant pieces of radical nationalist sentiment in Australian literature.
O'Dowd's later poetry explored the idea of sexual love, then he ceased writing poetry altogether. He lived with his companion, Marie Pitt (q.v.), after leaving his first wife in 1920. In 1934, O'Dowd declined a knighthood, but did not make this widely known. He died in 1953, several years after the death of Marie Pitt. The funeral oration was read by C. B. Christesen (q.v.) at the Springvale Crematorium, Melbourne on 3 September and Flora Eldershaw (q.v.) spoke on his work. O'Dowd was survived by his estranged wife and five sons.