He joined the SPD in 1920. In the aftermath of the 20 July plot of 1944 he was arrested. After World War II he became Senator of Hamburg. From 1950 to 1953, Nevermann was Second Mayor of Hamburg and as a successor of Max Brauer he was elected as First Mayor on 1 January 1961. During his term in office the North Sea flood of 1962 and the state visits of Charles de Gaulle (1963) and Elizabeth II (1965) were major events in Hamburg. During the visit of Elizabeth II the breakup with his wife became public and after a media campaign by the newspapers of Axel Springer Verlag Nevermann resigned in 1965.