John Marsden was born in Melbourne, the third of four children of Eustace Cullen Hudson and Jeanne Lawler Marsden. He attended Devonport Primary School in Tasmania and Eastwood Primary School and King's School, Parramatta, in New South Wales. Marsden began teaching at All Saints College, Bathurst, New South Wales, in 1978 while studying Arts at the University of New England. He continued to teach at All Saints while completing his Diploma of Teaching from Mitchell College.
In 1982 he became head of English at Geelong Grammar School, Highton, Victoria, and in 1984, rather to his own surprise, he found himself teaching at Timbertop, Geelong Grammar's 'bush' campus. Noticing a complete lack of interest in reading among his Year 9 students he tried writing a short novel that he thought they might enjoy. The novel, So Much to Tell You (1987), was immediately successful, winning the Children's Book Council of Australia (CBCA) Book of the Year: Older Readers in 1998 and other awards. Since publication, it has been translated into numerous languages and has had the largest sales for a book published in Australia for teenagers.
Marsden was regarded as Australia's most popular writer of novels for young adults, attributed to the seven-volume Tomorrow series series. In 1996, Marsden's books took the top six places on the Teenage Fiction best-seller lists for Australia. Also in 1996, he was named 'Australia's most popular author today in any literary field' by the Australian newspaper. In 1997 Australian readers voted three of his books into Australia's 100 most-loved books of all time. Tomorrow, When the War Began has been reprinted thirty times since its 1994 release, translated into multiple languages, and adapted as both a film and a television series.
Marsden also created picture book texts (most notably The Rabbits (1999), a CBCA Picture Book of the Year), poetry, and nonfiction. In 2015, The Rabbits was adapted as an opera by Kate Miller-Heidke and Lally Katz: The Rabbits opera was shortlisted for an International Opera Award, and won an AWGIE Award and three Helpmann Awards in Australia.
Marsden was a contemplative writer and popular speaker. His works invariably feature serious themes such as sexuality, violence in society, survival at school and in a harsh world, and conflict with adult authority figures. His teaching background added authenticity to his style, characterisation and themes.
Marsden was interested in sharing his understanding of the creative writing process itself. His Everything I Know About Writing (1993), Marsden on Marsden : The Stories behind John Marsden's Bestselling Books (2000) and a study of his own creative process for So Much to Tell You assist in an understanding of the writing process. While many of his fictional works are controversial in terms of their content, his nonfiction work, Secret Men's Business, is aimed at assisting young men in understanding their sexuality. Marsden sold a million and a half books world-wide, and won awards in Europe, America, and Australia.
Despite his success as a writer, Marsden always remained committed to the education process. He spent much of his time running writing camps at his property, the Tye Estate in Kerrie, Victoria. In 2006, he began operating a school, Candlebark, on the property. The school caters for children at primary and secondary level. In 2016, he opened an arts-focused secondary school, Alice Miller School, also in the Macedon Ranges. He was also patron of youth-media organisation Express Media, which offered the John Marsden Prize for Young Australian Writers annually since 2005.