Heinrich Ehmsen was born the fifth child of the basket maker Heinrich Ehmsen on 9 August 1886. His childhood is determined by poverty and his parents' struggle to earn their living.
Besides school, Ehmsen has to contribute to the family's livelihood from age five on by making baskets in the workshop of his father. From 1901 to 1906 Ehmsen is trained by Ernst Rüschmann, a master painter from Kiel. At the same time his first landscape and animal studies emerge. Ehmsen's interest in fine arts grows and he decides for a decorator's training, which he finances by himself by house painting after work. From 1906 to 1909 Ehmsen goes to the arts and crafts school in Düsseldorf, which has some leading representatives of Art Nouveau, like Peter Behrens and Jan-Thorn Prikker, among its teachers. At the end of his training he gets his first commission as a decorator: the design of two rooms of Düsseldorf's church art exhibition. In 1909 Ehmsen goes to Paris for a year, where he is inspired for his forthcoming creative work. He works freelance in Munich from 1911, the year he has to join up, until 1928, including a few breaks caused by World War I and several trips. Der blaue Reiter, a group of artists, starts to have an influence on his creative work, in addition to that his art is touched by social criticism. As a human being and artist, Ehmsen develops increasingly into a fighter for the miserable members of society, the revolution is the central idea of many of his pictures. After World War I his brooding over the war and the failed German revolution leads him to the madhouse studies. The insane prompt Ehmsen to depict how human existence is endangered and threatened. After a six month study visit in southern France Ehmsen moves to Berlin in 1929. The following year he works at the German academy in Rome together with Schmidt-Rottluff and Georg Schrimpf for six months and subsequently travels through southern Italy. In 1933 Ehmsen is held captive for several months by the Gestapo, in 1937 he is condemned as a degenerate artist and his paintings are removed from the German collections. During World War II Ehmsen is used as a soldier and a painter for the Wehrmacht, his house in Berlin, which contains many of his works, is destroyed. After the war Heinrich Ehmsen starts as a deputy principal and leader of a painting class at the academy of fine arts in West Berlin; in 1950, however, he changes over to the academy of arts in East Berlin.