Otto Braun (28 January 1872 - 14 December 1955) was a German Social Democratic politician, who was Prime Minister of Prussia.

Originally from Königsberg in East Prussia, Braun became a leader of the Social Democratic Party there, and was elected to the Prussian Diet in 1913. In 1919, he was elected to the Constituent Assembly in Weimar. He became most noted as Minister-President of Prussia, a position in which he served almost continually from 1920 to 1932. He was also the Social Democratic presidential candidate in the first round of presidential elections in 1925.

In the latter years of the Weimar Republic, Braun's Social Democratic led coalition government in Prussia was one of the strongest bastions of democracy. It was overthrown in a coup in July 1932 by the national government of Franz von Papen. Braun remained, however, in opposition to the new nationally appointed government of Prussia until after Hitler's appointment as Chancellor in January 1933, when he emigrated to Switzerland, where he died 22 years later.

After the end of WW II from his exile Braun approached the victorious allies to reinstate the legal Prussian government, but the occupation allies declined due to their plans to abolish the state of Prussia and of population transfer of Germans from large parts of that area.