He was born in the German city of Quedlinburg. At the age of fourteen, during a dangerous illness, he came under the personal influence of Johann Arndt, author of Das wahre Christenthum, and resolved to study for the church. He entered the University of Wittenberg in 1599, to study philosophy. He also attended lectures in theology, then changed to medicine for two years. In 1603, he resumed his theological reading at Jena, and in the following year received a new impulse from J.W. Winckelmann and Balthasar Mentzer at Marburg. He graduated in 1605 and began to give lectures at Jena, then in 1606 he accepted the invitation of John Casimir, Duke of Coburg, to the superintendency of Heldburg and mastership of the gymnasium; soon afterwards he became general superintendent of the duchy, in which capacity he was engaged in the practical work of ecclesiastical organization until 1616, when he became theological professor at Jena, where the remainder of his life was spent.
Johann Gerhard is still the dean of Theology after the Ring of Fire, and was known for his ability to smooth troubled waters and had studied medicine for several years in his younger days before turning to theology. Gerhard was among the gather deans that met with Dean Werner Rolfinck over the knowledge exchange with Grantville, in which he believed that this partnership will attract new students and refilling the faculty's ranks. But he was taken a bit surprised that women can be trained physicians and that the faculty would be met Grantville's medical representative Beulah MacDonald; however, he realized that it is inevitable that their university and practically their society must educate women, no matter what, with the progressive establishment of the New United States and then the United States of Europe.
Gerhard was later a part of the Jena delegation to Grantville in September, 1633. He bumped into Gary Lambert, who knew about Gerhard from history books. Gerhard's meeting with Lambert was affable. The next day, Lambert gave Gerhard a tour of the Leahy Medical Center. Gerhard was impressed with the building's architecture. He was more impressed upon seeing the hospital's staff working together and that both doctors and nurses were treated as equals. After finishing the tour, Gerhard considered telling the others in the Jena delegation about what he saw before taking another stroll in Grantville.
In March 1634, Gerhard was consulted with Werner Rolfinck over the numbers of ailing patients who were supernaturally healed by Pentecostal convert Dieter Fischer. The two deans had growing concerns about Dieter Fischer and the rising Pentecostal movement among the German population, including from some of their students, and feared of the possibilities that the Pentecostals were using their faith for a concerted demagogue. However, Gerhard see no theological evidence that it must be opposed at this point and instead to only cautiously watch the results of Fischer's congregational developments.