He was born Axél Waldemar Gallén in Pori, Finland. His father Peter Gallén worked as police chief and laywer. At the age of 11 he was sent to Helsinki to study at a grammar school. He also attended drawing classes at the Finnish Art Society.
In 1884 he moved to Paris, to study at the Académie Julian. In Paris he became friends with the Finnish painter Albert Edelfelt, the Norwegian painter Adam Dörnberger, and the Swedish writer August Strindberg.
In 1890 he married Mary Slöör. The couple had three children, Impi Marjatta, Kirsti and Jorma. On their honeymoon to Karelia, Gallen-Kallela started collecting material for his depictions of the Kalevala.
For the Paris World Fair in 1900 Gallen-Kallela painted frescoes for the Finnish Pavilion. He also painted the frescoes for the Jusélius Mausoleum in Pori between 1901 and 1903. The frescoes were destroyed during World War II but later repainted by the artist's son Jorma.
He officially finnicized his name to the more finnish sounding Akseli Gallen-Kallela in 1907.
In 1918 the regent, general Mannerheim invited Gallen-Kallela to design the flags, official decorations and uniforms for the newly independent Finland. In 1919 he was appointed Adjutant to Mannerheim.