Ernesti was born in Königsfeld[1] (Saxony), the son of the preacher Daniel Ernesti.[2] He received his first lessons from his father, who was a Königsfeldrector. Later, he attended high school in Altenburg under his cousin Jacob Daniel Ernesti. From 1670, he studied theology and philosophy at the University of Leipzig, where he became Baccalaureus in 1672, and in 1674 Master of Philosophy.
In 1680 he was appointed as an assessor at the Faculty of Arts of the University.[2] Furthermore, he worked until 1682 as a Saturday preacher at the Church of St. Nicholas. He was conrector (vice-principal) from 1680 and from 1684 to 1729 rector (principal) of the Thomasschule, succeeding Jacob Thomasius.[3] He introduced a new education policy, including allowing school prayer in German. He served for 45 years, the longest term of office of all known principals. His successor was the influential Johann Matthias Gesner.
From 1691 Ernesti was professor of poetry at the University of Leipzig. He taught about Roman poets Horace, Ovid, Juvenal and Virgil and also more recent Latin writers such as Helius Eobanus Hessus. Ernesti himself was active as a writer, his output included panegyrics. His most important work was 14 Selectarum Orationum Liber (Marcus Tullius Cicero).[4]
