Christiansen began teaching music at the Oberlin Conservatory in Oberlin, OH, where he founded the Oberlin A Cappella Choir in 1929. After obtaining a master of sacred music degree from Union Theological Seminary in 1940, he returned to his alma mater in 1941 to co-conduct the St. Olaf Choir with his father. Upon his father's retirement in 1943, he became the full time conductor of the St. Olaf Choir, a position he held until 1968
