The trained surveyor in 1869 jointly charged with his brother Alexander Forrest, perform an expedition into the hinterland of Western Australia. It should thereby explore the country and looking for traces of the missing German scientist Ludwig Leichhardt. After 19 weeks, which represented a constant battle against the dying of thirst, they returned without having found a trace of Leichhardt. However, they reported the numerous minerals and natural resources, which they had discovered - now located in this area profitable mining mines.
1870 were sent by Governor Frederick Weld to find a new land route from Perth to Adelaide. Again, the expedition crossed many desert areas, before they arrived at the destination. On this route one telegraph line was soon laid. Four years later, the next joint expedition of the brothers John and Alexander. From Geraldton on the west coast they set up in the central desert regions. On their way to the east they escaped nearly a raid by Aboriginal and were rescued by a surprising downpour from dying of thirst. However, they had the horses behind and came on foot to the running from Adelaide to the north telegraph route. This expedition was the first to Central Australia and the Victoria desert of west crossed to east.
In recognition of his achievements John Forrest received a prestigious position in the Western Australian government and 2000 acres of land on which he established a farm. In 1878 he undertook his last extended trip to the north-west coast, where he also explored various mine areas. 1890 was Forrest 's first prime minister of the self-governing colony from this year Western Australia and in 1901 a member of the first Australian federal government. In 1918, he was the first Australian titles of nobility, Baron Forrest of Bunbury.
After his health deteriorated this year, he decided to go to England to get medical treatment there. On July 30, 1918, he stood in Perth in the lake, but still died during the crossing.
According to him, one of Australia's oldest national park is named near Perth, the John Forrest National Park and the town of Forrest in the Nullarbor Plain.
- On 28 November 1949, the Australian Post issued a stamp in honor of John Forrest to 2 ½ d.
- 1994 Australia 5 Dollars commemorative coin, 925 silver, 35.79 g, 39 mm, Mint Canberra, edition 18,312 pieces