Yngvar Sonnichsen was born March 9, 1873, in Christiania (Oslo), Norway to S.P. Sonnichsen and his wife, Inga Mathea. He studied at the Polytechnic Institute in Oslo receiving a degree in civil engineering in 1894. He also studied art at the National School of Art and Design from 1894-1895. He returned to the same school in 1901-1902 as a student in the upper division where he worked and studied with the well-known Norwegian artists Hans Heyerdahl, Oscar Wergeland, and John Ekenaes. While in Norway, he became acquainted with Norwegian artist Edvard Munch as well as other artists such as Herbjørn Gausta, with whom he spent a summer sketching. He also studied in Antwerp and Brussels in the period 1895 and 1899 and at the Academic Julian in Paris with William Bouguereau and Benjamin Constant. When he returned to Norway, he studied with Eilif Peterssen in Lysaker. From 1900 until 1904 he painted portraits in Norway, had paintings accepted at several important exhibits, and worked as a designer for the institution which became the Norwegian Folk Museum. In 1904, Sonnichsen emigrated to St. John, New Brunswick, Canada. There he painted portraits and designed stained glass windows for churches in and around the area. He then moved to Vancouver, BC, where he supported himself doing commercial art. In 1908, he moved to Seattle, WA, where he painted portraits, landscapes and murals. While in the Seattle area, he helped support himself operating an orchard and doing house painting. In 1917, Sonnichsen painted murals for the Sons of Norway lodge in Seattle, in collaboration with Sverre Mach from Tromsø. Known especially for his portraits, he painted Ole Bull, Edvard Grieg, and Roald Amundson. Amundson was the model for his portrait which was completed in Seattle in 1922. In 1927, Sonnichsen painted a portrait of Martin Ulvestad while in Seattle. In 1933-34, he painted landscapes for the Seattle schools. For a while, Sonnichsen also lived in southeastern Alaska where he drew sketches and painted scenic landscapes. He became a naturalized US citizen in 1936. Sonnichsen married Agnes Gunhilde Andersen from Larvik,, in 1908 but she died five years later. He died in July 1938 in Seattle.