The team used camera traps and followed the bird's calls before catching it, removing some feathers and attaching an electronic tag. They have named it "Pedro", although it has not been verified whether it is male or female.
"For as long as we can, we'll keep it as secret as we can. It's just such a critical thing that we do everything that we can to save this species, to bring it back from the brink of extinction," said Rob Murphy, from the conservation group Bush Heritage Australia.
Nocturnal and nomadic, the parrot was discovered in 1845, but was barely seen again until a carcass was found by a roadside in western Queensland in 1990. Another carcass was found in 2006.
It was not until 2013 that John Young, a naturalist, claimed to have seen and documented a live bird in Outback Queensland. But the discovery proved controversial, with some critics claiming photographs had been retouched. However, Young passed on the location of the birds to several scientists, including Steve Murphy.
Experts estimate the population of the species is between 50 and 250.
Pedro was caught on April 4 and has been seen only once more, as the tracking tag is believed to have fallen off.
Birds on the brink
Jerdon's babbler: Until last year, the Burmese Jerdon's babbler had not been seen since 1941 but it was found at a research station set up to examine other species.
Worcester's buttonquail: Thought to be extinct, it re-emerged at a poultry market in Luzon, Philippines, in 2009 but was sold and eaten.
Ivory-billed woodpecker: A rare species which had not been seen in more than 50 years before a kayaker in Arkansas came across one in early 2004.
New Zealand storm petrel: Known only from three specimens collected in the 19th century, the storm petrel was photographed in 2003 and first examined two years later.