Background
Born in Copenhagen, Thomsen was the son of Chamber Councillor (kammerråd) Ludvig Frederik Thomsen and the brother of the acclaimed linguist Vilhelm Thomsen (1842–1927).
Born in Copenhagen, Thomsen was the son of Chamber Councillor (kammerråd) Ludvig Frederik Thomsen and the brother of the acclaimed linguist Vilhelm Thomsen (1842–1927).
After he had graduated in 1866, he began studying art with Frederik Vermehren the same year. He then attended the Royal Danish Academy of Fine Arts under Wilhelm Marstrand, graduating in 1871.
He specialized in genre painting and also illustrated the works of several Danish authors. He completed his studies in Italy at the end of the 1870s together with Kristian Zahrtmann and August Jerndorff. Thomsen exhibited in Carlottenborg from 1869.
Unlike some of his contemporaries, Thomsen did not follow any of the modern trends from Paris but maintain his Historicist approach, often painting literary subjects.
As an illustrator, he contributed woodcuts to both books and journals including works by Adam Oehlenschläger, Johan Ludvig Heiberg, Steen Steensen Blicher and Bachelor of Surgery Ingemann. In 1901, he became a professor of the Royal Danish Academy.