He served as the last Minister-President of Mecklenburg before its dissolution and thereafter as the longtime First Secretary of the Bezirk Schwerin SED before being forced into retirement in 1974.

He also briefly served as a member of the Landtag of the Free State of Mecklenburg-Schwerin on the eve of the Nazis' rise to power in 1932/1933.

[1] After the Nazis came to power in 1933, he was repeatedly detained and eventually interned from October 1939, first in the Sachsenhausen and from March 1940 in the Dachau concentration camp, where he was freed by French troops.

[1][4] From February 1948, he served as Minister of Agriculture of Mecklenburg in the cabinets of Wilhelm Höcker and Kurt Bürger,[1][3] succeeding Otto Möller, who left for a teaching position at the University of Rostock.

[1][3] During his time as First Secretary, Quandt successfully opposed the SED Politburo's decisions to construct multi-story prefabricated housing developments in rural areas, as he believed they would "ruin" the traditional village landscape.

[1][9] At the last session of the Central Committee on 3 December 1989, he tearfully[6][10] called for the reintroduction of the death penalty and the summary execution of all those (the "criminal gang of the old Politburo") who had brought disgrace (referring to the loss of power due to the revolutionary events in autumn 1989) upon the party (SED).