The theory of Portuguese discovery of Australia claims that early Portuguese navigators were the first Europeans to sight Australia between 1521 and 1524, well before the arrival of Dutch navigator Willem Janszoon in 1606 on board the Duyfken who is generally considered to be the first European discoverer. While lacking generally accepted evidence, this theory is based on the following:The Dieppe maps, a group of 16th-century French world maps, depict a large landmass between Indonesia and Antarctica. Labelled as Java la Grande, this landmass carries French, Portuguese, and Gallicized Portuguese placenames, and has been interpreted by some as corresponding to Australia's northwestern and eastern coasts. The proximity of Portuguese colonies in Southeast Asia from c. 1513–1516, particularly Portuguese Timor which is approximately 650 kilometres (400 mi) from the Australian coast. Various antiquities found on Australian coastlines, claimed by some to be relics of early Portuguese voyages to Australia but which are generally regarded as evidence of Makassan visit to Northern Australia.

Manuel Godinho de Erédia, or Emanuel Godinho de Erédia, was a Bugis-Portuguese writer and cartographer. He wrote a number of books, including an early account of the Malay Peninsula that is a source of information on the region of that period. In the early 17th century, he became interested in exploring a "southern land", which is thought to be Australia.