John Plummer was brought up near Whitechapel in a poor working-class family and was left deaf and crippled by an illness he suffered as a child. He taught himself to read and developed an interest in drawing and graphic design, later attending evening classes at the Spitalfields School of Design.
After his family moved due to unemployment, Plummer campaigned against the Northamptonshire Shoemakers' Union in 1858 for challenging the employment of one of his brothers. He subsequently published a pamphlet, Freedom of Labour. He continued to write a large number of pamphlets on many subjects, including 'self-help', workers' co-operatives, the evils of unions and strikes, social conditions, and literature. Plummer received support from Lord Palmerston who granted him £40 from the Royal Bounty Fund, and he also gained the favourable attention of Charles Dickens and others including J. S. Mill, who allowed Plummer to use his library. He worked as English social affairs correspondent for the Sydney Morning Herald, and in 1867 he was engaged to promote emigration in London.
After arriving in Australia to represent British exhibitors at the Sydney International Exhibition, he settled in Sydney where he worked as a journalist, editing and illustrating the Illustrated Sydney News and other papers. He also worked for several years on the Australian Town and Country Journal, lectured and published on technical education and applied arts, and was Fort Street Training School's drawing master from 1881 to 1890. During this time he wrote two books on art instruction, Technical Education : suggestions for a practical scheme intended principally for the artisan classes of New South Wales (1880), and Art Instruction (1880). He contributed on a wide range of topics to many major American, British and Australian newspapers, and wrote numerous guidebooks for Thomas Cook & Son.
Plummer was also active as a philanthropist, and assisted many charitable institutions. He was a member of the New South Wales Institute of Journalists and many other societies and organisations.