After the war Rosenthal contemplated not returning to the profession of architecture but did so while leading an active public life. From 1921–26 and also 1932–37 he was commander of the 2nd Division. He served as an alderman of Sydney Municipal Council in 1921–24 and was chairman of its works committee. He was also a Nationalist Party of Australia member for Bathurst in the New South Wales Legislative Assembly in 1922–25 and a member of the New South Wales Legislative Council in 1936–37. He was twice president of the Institute of Architects of New South Wales in 1926–30 and was also president of the federal council of the Australian Institutes of Architects in 1925–28. He also served as president of the Australian Museum, Sydney.