Oxley was born in England. After entering the Royal Navy as a midshipman he travelled to Australia in 1802 on the "Buffalo."

After years of trying to get an official position, he was appointed Surveyor-General of the colony in 1812 and in 1817 headed an expedition which explored the Lachlan, Macquarie, Castlereagh, Peel and Hastings Rivers. He named Port Macquarie, at the mouth of the Hastings, and returned down the coast to Sydney.

His work "Journals of Two Expeditions into the Interior of New South Wales " was the forerunner of a large body of exploration literature created by the men who explored inland Australia over the next half century.

In a subsequent expedition in 1823 he discovered the Tweed and Brisbane Rivers, and the site of the city of Brisbane, and in 1824 established a penal settlement at Moreton Bay.