He set up the New South Wales Red Cross Blood Transfusion Service, serving as its inaugural Director for twenty years from 1946 to 1966.
[1][3] When World War II broke out in September 1939, Walsh joined the Australian Army Medical Corps as a captain in the Citizen Military Forces.
He was diagnosed with hypertension and tuberculosis, which precluded him from serving overseas; instead, he led a domestic army unit which prepared blood serum for use by the military.
[2] As the BTS changed from civilian to military focus, Walsh left Sydney Hospital and joined the Army.
By July 1942, he was Commander of the newly created 2nd Australian Blood and Serum Preparation Unit, where he was promoted to Major in September 1942.
Under Walsh's direction, the unit developed innovative technology for blood transportation, such as identifying different requirements when it was shipped by air or sea.
Data from the BTS provided a unique opportunity to standardize instrument calibration, improving the accuracy of laboratory pathology measurements.
[5][1][2] By the early 1960s, the BTS was well established and had international credibility, so Walsh wanted to move on by getting involved in the new School of Medicine at the University of New South Wales (UNSW).
In 1962, Walsh was appointed UNSW's Visiting Professor of Human Genetics and before long he also chaired the university's Medical Research Advisory Committee.
[6][2] In 1966, he resigned from the BTS to assume a full-time position as foundation chair and Professor of Human Genetics at the UNSW.
[3][1] In the 1982 Queen's Birthday honours, Walsh was appointed Companion of the Order of Australia (AC) "for service to medicine".
[2] Walsh suffered from hypertension throughout his career, and a severe episode in 1953 resulted in ongoing problems with his vision and kidneys.