Fohr began to study painting largely on his own after a short training with Friedrich Rottmann. The Darmstadt artist and Councillor George William Issel discovered him in 1810 and in 1811 invited him to Darmstadt. There he met the Chamber's secretary and historian Philip Dieffenbach, who was acquainted with the Princess Wilhelmine Luise von Baden. After being introduced to her, the princess became one of his financial supporters and art sponsors.

Later he studied at the Academy in Munich, where he met the art student Ludwig Sigismund Ruhl and studied oil painting. He interrupted his studies there prematurely to visit northern Italy and later also Rome. There, he worked briefly among the Nazarenes and was influenced by Peter von Cornelius, Philipp Veit and Friedrich Overbeck, but, increasingly started to develop his own style. In Rome, he shared a studion with the Tyrolean landscape painter Joseph Anton Koch, whose work influenced his style.

One of his most important work is the sketch of a group of German artists in Rome, in the Café Greco. On 29 June 1818 Fohr drowned while bathing in the Tiber.

His younger brother Daniel Fohr was also a landscape painter, holding, at times, the position of the Baden court painter. Fohr was the great - great uncle of the painter Christian Schad.