Candael was very active in the local choral movement. He founded De Zangkapel choir in 1904 and started organizing events in Antwerp. The same year, Karel debuted as a composer and wrote the symphonic poem Levensdroom (Dream of Life) and Genoveva van Brabant cantata. Some of his best-known compositions include ballets De Zeven Hoofdzonden (1927) and Het Hooglied (1936), and the oratorio Het Marialeven (1941–43).

In 1909, Candael became the second conductor of the Orkest Van De Koninklijke Vlaamse Opera. Two years later, Karel started performing as a conductor at the Koninklijke Nederlandse Schouwburg Theater in Antwerp. He continued working at the Royal Flemish Opera as a first conductor in the mid-twenties.

As an educator, Karel Candael began his career at the Royal Conservatoire of Antwerp in 1919. He was one of the candidates for a director's position after Mortelmans retired in 1933, but lost the nomination to Flor Alpaerts.