(6 January 1870 – 16 September 1944) was a German Social Democratic Party leader and Chancellor of Germany from 1919 to 1920.

Born in Darkehmen (now Ozyorsk, Kaliningrad Oblast) near Königsberg in East Prussia, Bauer, who rose to notice through his leadership of a white-collar trade union, served from 1908 to 1918 as chairman of the General Commission of Trade Unions for all of Germany. A member of the Reichstag, Bauer entered Prince Max of Baden's government in October 1918 as Minister of Labour, a role which he continued to hold in the government of Philipp Scheidemann after the war. When Scheidemann resigned in June 1919 to protest the Treaty of Versailles, Bauer became Chancellor, serving until March 1920, when he resigned shortly after the failure of the Kapp Putsch.

Bauer resigned from the Social Democratic Party and the Reichstag in disgrace in February 1925, after it appeared that he had accepted improper payments in the Barmat Scandal and then lied about it, but was reinstated in 1926.

Bauer later served in the governments of Hermann Müller and Joseph Wirth.

Cabinet June 1919 - March 1920

• Gustav Bauer (SPD) - Minister-President (after 14 August 1919 Chancellor)
• Matthias Erzberger (Z) - Vice Chancellor and Finance Minister
• Hermann Müller (SPD) - Foreign Minister
• Dr. Eduard David (SPD) - Interior Minister
• Rudolf Wissell (SPD) - Economics Minister
• Robert Schmidt (SPD) - Food Minister
• Dr. Alexander Schlicke (SPD) - Labour Minister
• Dr. Johannes Bell (Z) - Transportation Minister and Colonial Minister
• Johannes Giesberts (Z) - Postal Minister
• Wilhelm Mayer (Z) - Treasury Minister
• Gustav Noske (SPD) - Defence Minister

Changes

• July 15, 1919 - Robert Schmidt succeeds Wissell as Economics Minister. Schmidt remains Food Minister.
• October 3, 1919 - Dr. Eugen Schiffer (DDP) enters the cabinet as Justice Minister and succeeds Erzberger as Vice-Chancellor. Erzberger remains Finance Minister. Dr. Erich Koch-Weser (DDP) succeeds David as Interior Minister. David remains in the cabinet as Minister without Portfolio.
• October 25, 1919 - Otto Gessler (DDP) enters the cabinet as Reconstruction Minister.
• November 7, 1919 - The Colonial Office is abolished. Bell remains Transportation Minister.
• January 30, 1920 - Mayer resigns as Treasury Minister.
• March 12, 1920 - Erzberger resigns as Finance Minister.