August Eisenmenger was an Austrian painter of portraits and historical subjects.
He was born in Vienna. At the age of fifteen, Eisenmenger was already a student at the Academy of Fine Arts Vienna and won first prize in drawing. In 1848, his financial circumstances forced him to leave the Academy. He didn't find a secure position until he became a student/employee at Carl Rahl's studio in 1856.

In 1863, he became a drawing teacher at the Protestant School in Vienna. He eventually obtained a professorship at the Academy in 1872. He also established a private school where he taught Rahl's style of monumental painting. Rudolf Ernst was one of his best known pupils there.

He died in Vienna in 1907. In 1913, a street in Vienna's Döbling district was named after him. Later, that street was removed for an industrial site and a new street was dedicated to him in the Favoriten district in 1959.

One of Eisenmenger's sons, Victor Eisenmenger, was the personal physician to Archduke Franz Ferdinand.