Karl Heinzen (1809–1880) was a German-born revolutionary writer, journalist, and political exile whose career bridged the upheavals of Europe and the radical press culture of the United States. A participant in the failed movements leading up to the Revolutions of 1848, he fled the German states and eventually settled in Boston, where he became a leading voice among German-American radicals.

Heinzen edited and contributed to several German-language newspapers, using them as platforms for uncompromising critiques of monarchy, organized religion, and social conservatism. He was an early and forceful advocate of republican government and individual liberty, and his writings often pushed beyond mainstream reform into explicitly revolutionary territory. Notably, he defended the use of political violence against tyrannical regimes, a position that made him both influential and controversial among fellow exiles.

In the United States, Heinzen remained active in abolitionist and reform circles, aligning himself with the more radical edge of mid-nineteenth-century political thought. His career reflects the transatlantic flow of revolutionary ideas and the role of immigrant intellectuals in shaping American dissenting traditions.