Ewans played initially as a banjoist, but switched to saxophone in 1923 when he formed the Blues Jazz Band. The group disbanded in 1924, after which Ewans joined Valdemar Eiberg's ensemble from 1924–26. He adopted the name Kai Ewans in 1927, and led Denmark's first big band in 1927–28, thereafter leading bands in Belgium and Germany through 1931. Following this he played with Bernard Etté, Kai Julian (1931–32), and Eric Tuxen (1932–36). He founded a new big band including mostly musicians from Tuxen's ensemble in 1936, and recorded copiously with Benny Carter in the 1940s. The ensemble dissolved in 1947, and after this Ewans worked in business in the U.S., moving to California in 1956. From 1960 to 1964 he ran a restaurant with Carter in Beverly Hills, and later in the decade returned to Copenhagen to play again. He retired to Connecticut late in life.
- Erik Wiedemann, "Kai Ewans". The New Grove Dictionary of Jazz.