Archduke Franz Karl Joseph of Austria (17 December 1802 – 8 March 1878) was a member of the House of Habsburg-Lorraine.

Through his third son Karl Ludwig, he was the grandfather of Archduke Franz Ferdinand of Austria – whose assassination sparked the hostilities that led to the outbreak of World War I. Franz Karl was born in Vienna, the third son of Emperor Francis II of the Holy Roman Empire by his second marriage with Princess Maria Theresa from the House of Bourbon, daughter of King Ferdinand I of the Two Sicilies and Maria Carolina of Austria.

Sophie's paternal half-sister, Caroline Augusta of Bavaria was by this time Franz Karl's stepmother, having married his thrice-widowed father in 1816.

Franz Karl was an unambitious and generally ineffectual man, although he was, together with his uncle Archduke Louis, a member of the Geheime Staatskonferenz council, which after the death of Emperor Francis II ruled the Austrian Empire in the stead of his mentally ill brother Ferdinand from 1835 to 1848.

Franz Karl was the last Habsburg whose viscera were entombed at the Ducal Crypt of St. Stephen's Cathedral and whose heart was placed at the Herzgruft of the Augustinian Church according to a centuries-long family rite.