Karl Friedrich Bahrdt (August 25, 1741 - April 23, 1792), German theologian and adventurer, was born at Bischofswerda, where his father, afterwards professor, canon and general superintendent at Leipzig, was pastor.

At the age of sixteen young Bahrdt, a precocious lad whose training had been grossly neglected, began to study theology under the orthodox mystic Christian August Crusius (1715-1775), who in 1757 had become first professor in the theological faculty. The boy varied the monotony of his studies by pranks which revealed his unbalanced character, including an attempt to raise spirits with the aid of Dr Faust's Höllenzwang. His orthodoxy was, however, unimpeachable, his talent conspicuous, and in 1761 he was appointed lecturer on biblical exegesis, and preacher (Katechet) at the church of St Peter. His eloquence soon gave him a reputation, and in 1766 he was appointed professor extraordinarius of biblical philology. Two years later, however, the scandals of his private life led to his dismissal.

In spite of this he succeeded in obtaining the chair of biblical antiquities in the philosophical faculty at Erfurt. The post was unpaid, and Bahrdt, who had now married, lived by taking pupils and keeping an inn. He had meanwhile obtained the degree of doctor of theology from Erlangen, and was clever enough to persuade the Erfurt authorities to appoint him professor designate of theology. His financial troubles and coarse and truculent character, however; soon made the town too hot to hold him; and in 1771 he was glad to accept the offer of the post of professor of theology and preacher at Giessen.

Thus far Bahrdt's orthodoxy had counterbalanced his character; but at Giessen, where his behaviour was no less objectionable than elsewhere, he gave a handle to his enemies by a change in his public attitude towards religion. The climax came with the publication of his Neueste Offenbarungen Gottes in Briefen und Erzählungen (1773-1775), purporting to be a "model version" of the New Testament, rendered, with due regard to enlightenment, into modern German. The book is remembered solely through Goethe's scornful attack on its want of taste; its immediate effect was to produce Bahrdt’s expulsion from Giessen.

He was lucky enough at once to find a post as principal of the educational institution established in his château at Marschlins by the Swiss statesman Ulysses von Salis (1728-1800). The school had languished since the death of its founder and first head, Martin Planta (1727-1772), and von Salis hoped to revive it by reconstituting it as a "Philanthropin" under Bahrdt's management. The experiment was a failure; Bahrdt, never at ease under the strict discipline maintained by von Salis, resigned in 1777, and the school was closed. At the invitation of the count of Leiningen-Dachsburg, Bahrdt now went as general superintendent to Durkheim on the Hardt; his luckless translation of the Testament, however, pursued him, and in 1778 he was suspended by a decision of the high court of the Empire. In dire poverty he fled, in 1779, to Halle, where in spite of the opposition of the senate and the theologians, he obtained through the interest of the Prussian minister, von Zedlitz, permission to lecture on subjects other than theology. Forced to earn a living by writing, he developed an astounding literary activity. His orthodoxy had now quite gone by the board, and all his efforts were directed to the propaganda of a "moral system" which should replace supernatural Christianity.

By such means Bahrdt succeeded in maintaining himself until, on the death of Frederick the Great, the religious reaction set in at the Berlin court. The strain of writing had forced him to give up his lectures, and he had again opened an inn on the Weinberg near Halle. Here he lived with his mistress and his daughters--he had repudiated his wife--in disreputable peace until 1789, when he was condemned to a year’s imprisonment for a lampoon on the Prussian religious edict of 1788. His year's enforced leisure he spent in writing indecent stories, coarse polemics, and an autobiography which is described as "a mixture of lies, hypocrisy and self-prostitution." He died on the 23rd of April 1792.

See life, with detailed bibliography, by Paul Tschakert in Herzog-Hauck, Realencyklopädie; a more favourable account is given in JM Robertson 's Short History of Freethought, ii. 278.