He is best known for his work testing the effects of mustard gas on Australian troops in tropical conditions during World War II.

This organisation, formed as a grassroots and industry-focussed alternative to the existing scientific societies, was disbanded in 1949 as a result of political attacks founded in Cold War hysteria.

[12] This included physiological research on the effects of mustard gas trials on Australian Defence Force volunteers in Townsville, North Brook Island, Proserpine and Mission Beach.

Legge and a fellow biochemist (later Prof. Sir) Hugh Ennor designed and oversaw the construction of a 100 cubic metres (3,500 cu ft) stainless steel temperature-controlled gas chamber.

[6] Legge described the work as "grisly" but necessary, because it was known that the Japanese armed forces had large stocks of this gas, and that tropical heat and humidity would render it more effective in use than it had been on the Western Front in World War I.

[6] This included the official photographer of the project, who developed severe chronic respiratory problems owing to his occupational exposure to the gas, from which he later died.

Legge was granted a fellowship which enabled him to spend two years in England, working at the Molteno Institute, Cambridge University under Professor David Keilin who, in the early 1930s had been an associate of Rudi Lemberg before his departure to Sydney in 1935.

[16] Despite earning the esteem of his colleagues, his obvious passion for teaching, and his flair for research, the highest position Legge achieved was that of senior lecturer.

[18] Legge joined the Communist Party of Australia (CPA) in 1935 or 1936 and helped distribute the Tribune at a time when the newspaper was banned.

[20][15] He was extensively questioned about an alleged 1950 meeting with his cousin George Legge who worked for the Department of External Affairs in Canberra at the time.