Forrest was born in Perth, Western Australia, the youngest of three children of Judith (née Fry) and Donald Forrest. His father, grandfather (Mervyn), and great-grandfather (David) were all managers of Minderoo Station, which David had established in 1878 with his brothers, Alexander and John. John, Alexander, David, and Mervyn were all members of parliament for periods, with John serving as Western Australia's first premier. Forrest's early years were spent at Minderoo, located in the Pilbara region south of Onslow. Minderoo was owned by the Forrest family until it was sold in 1998 by his father due to relentless drought and debt, but it was bought back by Forrest in 2009.