Theodor Olshausen (1802–1869) was a German writer, journalist and politician, prominent in the Patriotic Party of Schleswig-Holstein.

Olshausen was born at Glückstadt, studied law at Kiel and Jena, and, for his part in the demagogic disturbances, was forced to live in France and Switzerland until 1830.

He was imprisoned in 1846 for his bold opposition, but his influence was all the stronger in the Revolution of 1848, and he became a member of the provisional Government, resigning to enter the Diet.

In 1851 he was excluded from the amnesty, went to America, and lived in New York City and St. Louis.

In the latter city, he was the editor-in-chief of the Westliche Post during the American Civil War.