Lennart Rafael Segerstråle was born in Vantaa, Finland on June 17, 1892. His father, Knut was an academic, his mother, Hanna Frosterus Segerstråle was a painter and his sister Solveig von Schoultz a noted Finnish poet, and author.

Lennart graduated from college in forest management in 1915 but in 1919 decided instead to become an artist. He had studied art at the University of Helsinki and in Copenhagen. He returned to school and graduated from the Det Kongelige Akademi for de Skønne Kunster in 1929.

Segerstråle exhibited in Finland between 1913 and 1967 and also participated in international exhibitions. He painted numerous altarpieces and did stained glass windows for churches in Finland. His magnum opus are the frescoes he painted for the head offices of the Bank of Finland in Finlandia.

Lennart Segerstråle died on April 11, 1975 in Porvoo, Finland.