Son of an Adelaide lawyer, Johnson moved with his family to Victoria in the early 1850s and was educated at Geelong National Grammar School. Leaving school at the age of sixteen he spent a few years in 'pastoral employment' and mining before turning to journalism. He returned to Adelaide in 1868 and joined the staff of The Register, where he was dramatic critic 1873-1880. In 1880 he purchased and edited the Adelaide Punch. In 1884 he was elected as Member for Onkaparinga in the South Australian Legislative Assembly and from 1887-1889 was Minister of Education.

He contributed to the Savage Club Annual, the Adelaide Miscellany and the South Australian Christmas Annual, and published collections of short stories and poems in the form of tales told around the camp fire by workers in the outback. He also published an autobiographical account of a journey to the Mount Browne goldfields, To Mount Browne and Back : or, Moses and Me (c.1866) and wrote a number of books on gold mining, his book Getting Gold being republished in England and the United States.

Johnson's varied interests included travel, music, literature and art and he was a member of the council of the South Australian School of Mines and Industries and also the Public Library, Museum and Art Gallery of South Australia board.