Characterized by simple harmonies, march rhythms and an appealing melodic style, his music is reflective upon the musical ideas favoured by the Stalinist regime of the 1940s and 1950s.
His first cousin was the composer, organist and music teacher Villem Kapp.
Four years later he joined the adjunct faculty at the Conservatory where he taught music theory and composition.
He won the Stalin Prize in 1946 for his opera Tasuleegid (‘Fire of Revenge’).
From 1948 to 1965, Kapp served as chairman of the Estonian Composers' Union.