Conrad, a distinguished historian and geographer, was born at Altdorf in Bavaria, in 1756. After completing his studies at the venerable university of his native town, he was appointed professor in the principal educational institution of Nürnberg, a position which he exchanged in 1788 for that of rector of the gymnasium of St Gilles in the same city. In 1797 Mannert was elevated to the chair of philosophy in the university of Altdorf; and in 1808 he went to Landshut in the capacity of professor in ordinary of history, with the title of Aulic Counsellor; but this university being suppressed in 1826, he was appointed professor of geography and statistics at Munich, a situation which he held till his death in 1834.

As a historian Mannert is distinguished for accuracy and critical exactness. He verified his facts with the most scrupulous care, and he has become, in consequence, a weighty authority on geographical and historical subjects.

His Geography of the Greeks and the Romans is his most popular work, and is always referred to as a standard authority on that subject. His works are:—Gesch. der Vandalen, Leipzig, 1785; Gesch. der Nachfolger Alexanders, Leipzig, 1787; Miscellanea, Nürnberg, 1793; Geographie der Griechen u. Römer, Leipzig, 1788-1825; Compendium der deutschen Reichsgesch. Leipzig, 1803; Statistik des deutschen Reichs, Bamberg, 1805; Die älteste Gesch. Bojoariens, Nürnberg, 1807; Kaiser Ludwig IV., Landshut, 1812; Handbuch der alten Geschichte, Berlin, 1818; Der Gesch. Baierns, 1826.