Karl Friedrich was the son of Hereditary Prince Friedrich of Baden and Anna of Nassau-Dietz-Orange (October 13, 1710 – September 17, 1777), the daughter of William Friso of Nassau-Dietz-Orange.
Born on 22 November 1728 in Karlsruhe, Karl Friedrich was the son of the Kronprinz of Baden, Friedrich von Baden-Durlach (1703-1732) and of Anne Charlotte von Nassau-Dietz-Orange (1710-1777).
Margrave of Baden-Durlach, Karl Friedrich inherited the branch of Baden-Baden in 1771, became elector of Baden in 1803 and Grand-Duke in 1806. His first marriage, in 1751, was to Princess Caroline de Hesse-Darmstadt (1723-1783). In 1787 he married Luise Geiger (1768-1820), who became Comtesse von Hochberg in 1796 and Princess of Baden in 1817, with whom he was to have ten children.
Almost the quintessence of the enlightened despot, Karl Friedrich Margrave of Baden lived through and participated in all the changes of the Enlightenment, the Revolution and the Napoleonic period. During his 65-year reign he improved agriculture, abolished torture in 1767 and serfdom in 1783, and in the years after 1803, guided by his minister Brauer, modernised Baden administration, creating an all-powerful state machine.
Despite being on the losing side in the wars of 1793 against France, Karl Friedrich was favourably treated by the Revolutionary committee and in a 1796 treaty aligned himself closely with France. He consented not only to the seizure of the lands on the left Bank of the Rhine (immediately opposite Baden on the right bank) but also allowed French troops free passage through the margravate. The Revolution for its part promised not to support Badish Jacobins. During the war of the Second Coalition Baden adopted a position of frightened neutrality. Regardless of the apparent lack of support, Napoleon increased Baden in size in order to make it a middle-sized state, powerful enough to support French policies in Germany and as a possible ally and counter weight to Austria. In the decade 1800-1810, Napoleon increased Baden in size four times, from 3,600 to 15,000 km2. Karl Friedrich was to benefit particularly from the Reichsdeputationshauptschluss (a meeting called to regulate the compensation to given to the different German states which had lost land when the left bank of the Rhine became French). Part of the reason for this was that Karl Friedrich's granddaughter had married Czar Alexander I and the dispositions presented at the meeting had been decided by France and Russia. Karl Friedrich was also to become Elector and proportionally speaking, Baden was to receive the best compensation for its loss of territory and people. Two years later, Karl Friedrich was to be further honoured. After having signed an alliance with Napoleon in September 1805, promising three thousand troops, Karl Friedrich was handsomely rewarded for his loyalty with the "upgrade" by Napoleon of his land to a Grand Duchy and the signing of a perpetual alliance with France, Italy and Bavaria – although Karl Friedrich was disappointed not to receive the title of "king". Encouraged by Napoleon, Karl Friedrich then mediatised (in other words, swallowed up) the smaller religious and chivalric state within Badish borders. Then on 4 January 1806, with Bavaria and Wurtemburg, he joined in perpetual political and military alliance with France and effectively broke with the constitution of the Holy Roman Empire (although nothing was done legally at this point). The final piece in the alliance jigsaw was the marriage of Josephine's niece, Stephanie de Beauharnais to Karl Ludwig Friedrich, Kronprinz of the Grand Duchy (Karl Friedrich's grandson), in the late spring. This marriage was to confirm Baden in its loyalty to France and in its position as bridgehead of the French Empire in France. This was followed by Baden accession to the Confederation of the Rhine on 12 July of the same year. Whilst the treaty gave Baden certain territories (the county of Bonndorf and the town of Tüttlingen) and took away others (notably the town of Biberach), the most important feature was that Baden had to put at Napoleon's disposal 8,000 troops for any continental war in which he might be engaged. Hence when Prussia mobilised against France in the late summer of 1806, Baden was called upon to honour her obligations. The Badish army (organised along French lines) was also to serve in Spain and Russia, suffering heavy losses alienating many, a fact which left the people out of step with the pro-French court. However as the first decade came to an end, Karl Friedrich entered his dotage and political and administrative matters were run by his minister Sigismund Freiherr von Reitzenstein, ruler of the state in all but name. He died in 1811, before the end of the First Empire, and was succeeded by his grandson, Karl Ludwig Friedrich.