Between 1857 and 1865, Macadam served as honorary secretary to the Exploration Committee of the Royal Society of Victoria, which organised the Burke and Wills expedition.
The expedition was organised by the society with the aim of crossing the continent of Australia from the south to the north coasts, map it, and collect scientific data and specimens. At that time, most of the interior of Australia had not been explored by the European settlers and was unknown to them.
In 1860–61, Robert O'Hara Burke and William John Wills led the expedition of 19 men with that intention, crossing Australia from Melbourne in the south, to the Gulf of Carpentaria in the north, a distance around 2,000 miles.
Three men ultimately travelled over 3,000 miles from Melbourne to the shores of the Gulf of Carpentaria and back to the Depot Camp at Cooper Creek. Seven men died in the attempt, including the leaders Burke and Wills. Of the four men who reached the north coast, only one, John King, survived with the help of the indigenous people to return to Melbourne.
This expedition became the first to cross the Australian continent. It was of great importance to the subsequent development of Australia and could be compared in importance to the Lewis and Clark Expedition overland to the North American Pacific Coast to the development of the United States.
After the heavy death toll of the expedition, initial criticism fell on the Royal Society, but it became clear that their foresight could not have prevented the deaths and this was then widely recognised when it became known that as Secretary of the Exploration Committee of the Burke and Wills expedition, Dr. Macadam had insisted on adequate provisions for their safety.