Theodor Barth (16 July 1849 – 3 June 1909) was a German liberal politician, publicist and economist.

[4] Barth started his political career with the National Liberal Party.

To that end, he sought the cooperation of the Social Democrats,[4] and at multiple times voted against his own party.

In the German Freeminded Party (Freisinnige Partei), founded in 1884, Barth would soon find himself opposed to the leadership of Eugen Richter.

Barth however would found the Democratic Union[4] (Demokratische Vereinigung) in 1908, together with Rudolf Breitscheid and Hellmut von Gerlach, after the Freeminded Union's participation in the Bülow-Block coalition in the 1907 elections.