Remak, born the son of a shopkeeper in Posen (now in Poland), obtained his MD from the University of Berlin in 1838. Although he spent most of his career there and despite his considerable scientific achievements Remak was denied appropriate promotion and a teaching position because he was a Jew.

In 1838 Remak finally disposed of the ancient myth, probably dating back to Alcmaeon of Croton, that nerves were hollow tubes. In the long history of medicine they had been authoritatively described by centuries of keen-eyed anatomists as carrying various spirits, fluids, and airs. Even the introduction of the microscope in the 17th century made no difference. It was left to Remak to point out that the nerve fiber is not hollow, but solid and flat.

In 1844 Remak discovered ganglion cells in the heart, thus showing that it could maintain a rhythmic beat independently of the central nervous system. He further noted that certain fibers of the nervous system, the sympathetic fibers, have a distinctly gray color rather than the more common white. They in fact lack the myelin sheath enclosing other nerve fibers.

In the mid 1840s, in collaboration with Johannes Müller, Remak made a major revision to the orthodox embryology of Karl von Baer. They reduced the four germ layers of von Baer to three by taking the two middle layers as only one. They also at this point introduced the modern terminology of endoderm, mesoderm, and ectoderm.

It was also Remak who, in 1841, first fully described the process of cell division. He went on to insist that the nucleus was a permanent feature of the cell even though it did become less noticeable after cell division. By 1855 Remak was ready to assert the general conclusion implicit in much of the early cell theory: that the production of nuclei or cells is really only division of preexisting nuclei or cells.