Joanne Van Os grew up in Melbourne, the eldest of six children born to Martin and Therese van Os. Her Dutch immigrant father's love of the bush and all things to do with nature was a strong influence on her, and after completing Year 12 in 1972 at Aquinas College in Ringwood, she worked for three years studying zooplankton and the effects of heavy metal pollution on them, with Victorian Fisheries and Wildlife.
Van Os was married for a decade to Rod Ansell whose life inspired the film character, Crocodile Dundee. Her memoir Outback Heart is the story of her life with this "Real Crocodile Dundee", their adventures living in the remote parts of the Territory, and his subsequent spiral into tragedy. After her marriage to Rod Ansell ended she met Lex Silvester in 1991. They married and had a daughter. Van Os and Silvester have lived on their yacht Tramontana in the Darwin marina, in the Northern Territory.