August Jernberg was a Swedish artist. He was a member of the Düsseldorf school of painting.

He was mainly a painter of portraits in his early years; he also painted historical and biblical pictures. In the 1860s he became a genre and landscape painter. He studied at the Royal Swedish Academy of Fine Arts in Stockholm from 1843–46 and then traveled to Paris, where he studied from 1847-53 with Thomas Couture (1815–1879).

He exhibited at the Scandinavian Art Exhibition at Stockholm in 1850 and at the Exposition Universelle (1855) at Paris. In 1854, he settled in Düsseldorf and was admitted as a member to the Kunstakademie Düsseldorf. He remained in Düsseldorf until his death, with the exceptions of some shorter trips.

In 1848, he married Margareta Bjurling (1823-1903). They were the parents of several children including their son Olof Jernberg (1855–1935) who was a German landscape and marine painter.