Owing to his extensive learning he was soon useful to Gottfried Leibniz, who in 1694 took Eckhart as assistant, and was, until death, his large-hearted patron and generous friend. Through the efforts of Leibniz, Eckhart was appointed professor of history at Helmstedt in 1706, and in 1714 councillor at Hannover.
Not long after this, Johann Philipp von Schönborn, Bishop of Würzburg appointed Eckhart his librarian and historiographer. In his work Eckhart was influenced by the new school of French historians, and gave careful attention to the so-called auxiliary sciences, above all to diplomatics; he also strove earnestly to follow a strictly scientific method in his treatment of historical materials. Together with Leibniz he is considered a founder of modern historiography in Germany.
Besides the help he rendered Leibniz, of whom he edited the Collectanea Etymologica (1717) and prepared an affectionately respectful obituary (in Christoph Gottlieb von Murr, Journal für Kunstgeschichte, VII), he issued a number of independent works. His chief work, while professor at Helmsted, is his Historia studii etymologici linguae germanicae haetenus impensi Hanover, 1711), a literary and historical study of all works bearing on the investigation of the Germanic languages. At Hanover he compiled a Corpus historicum medii aevi (Leipzig, 1723), in two volumes; at Würzburg he published the Commentarii de rebus Franciae Orientalis et episcopatus Wirceburgensis (1729), also in two volumes.
^J. G. Eckhart, Beschreibung desjenigen, was bey Grabung des Herrenhäuser‐Canals am Lein‐Strome her Curiöses in der Erde gefunden worden, Neue Zeitungen von Gelehrten Sachen auf das Jahr 1719
Nr. 24, 185–192, see Cornelius Steckner: Lügenstein und Weltarchäologie[permanent dead link].