Magnussen was born on 2 April 1885 in Copenhagen, the son of bookkeeper Sophus Oscar M. (1849–1926) and Christiane Marie Weybøll (1853–1930).
[1] Magnussen was a strong defender of the naturalistic style at a time when modernism came to play a still more dominant role on the art scene.
November and Foreningen for National Kunst, He was an art critic at København (1920–26), Nationaltidende and other newspapers.
[1] His writings included his memoirs Billedhugger-Minder (1933), monographies about Janus la Cour (1928), Carl Bloch (1931), Christian Molsted (1935), Svend Hammershøi (b.
[1] Magnussen married royal translator Ellen Reck (6 May 1879 – 9 January 1956), a daughter of military officer and businessman Anders Borch R. (1850–1927) and Marie Johanne Jacobine Qvist (1854–1927), on 10 July 1912 in Hellerup.