The assayers said that the Reef had contributed 6.4 billion dollars to the Australian economy in 2015 and 2016 combined, supporting 64,000 jobs including 33,000 in the state of Queensland.
"This timely report is a much needed, holistic view of the incredible economic value and opportunities provided by the Great Barrier Reef", he said.
"But when you look beyond that and think well what individual benefits do people get for recreational use and what do the broader society get, that's more significant as a contributor and that's how we came up with that figure of 56 billion Australian dollars".
There is a lot the business and scientific communities can do on the issue of climate change O'Mahony stressed, and added that the objective of the study is to show just how precious the Great Barrier Reef is to all Australians, and the globe as a whole. He also called it "a bigger employer than many well-known Australian companies, including Qantas Airlines".
But it ascribes nearly as much - $24bn - to Australians who are yet to see it but value knowing that it exists.
"As the largest living structure on earth and one of the world's most complex and diverse natural ecosystems, the Great Barrier Reef is justifiably considered priceless and irreplaceable".
The study included a survey of 1,500 Australian and global respondents from 10 countries that found people value the reef for a range of reasons - due to its importance for tourism but also the belief that Australia would not be the same without it.
"Two consecutive years of global coral bleaching are unprecedented, while increasingly frequent extreme weather events and water quality issues continue to affect reef health", said Dr John Schubert AO, Chair of the Great Barrier Reef Foundation.
"The water temperature is picking up and if you don't have coral reefs that are resilient, well they're dying, and more of that is going to happen over the coming years", O'Mahony said.
"That's more than 12 Sydney Opera Houses, or the cost of building Australia's new submarines".
It is also under pressure from farming run-off, development and the crown-of-thorns starfish, with the problems compounded this year by a powerful cyclone pummelling the area.
The report follows a summit held in May by the Australian government with marine experts to draw up a plan for how best to tackle the destruction of the Great Barrier Reef.