He was active from 1919 to 1960 and won Academy Awards for Best Art Direction for Wilson (1944) and Blood on the Sun (1945).

[3] He worked for a time as the assistant to a prominent New York architect and studied architecture at Columbia University.

[3][4] Ihnen first worked in the motion picture business in approximately 1919 at Paramount Studios on Long Island.

[3] One of his earliest works as an art director was the Josef von Sternberg's 1932 film, Blonde Venus.

Ihnen received his first Academy Awards nomination for Best Art Direction on Every Day's a Holiday.