Holmboe's musical development was cosmopolitan. He studied in Denmark, with Toch in Berlin and in Romania, where he came into contact with Balkan folk music and heard the works of Béla Bartók whose style he assimilated. On returning to his homeland he continued to work as a composer and critic and was professor at the Royal Danish Conservatory from 1950 - 1965 where he became immersed in Medieval church music. Holmboe's approach, with its free use of melodic and diatonic patterns was, however, basically neo-Classical, though more austere and inward-looking than either Nielsen or Sibelius, whose influence is less evident than that of Stravinsky and Bartók. The First Symphony (1935) is a work of chamber proportions, while the third and fourth (a choral work), respectively subtitled "Sinfonia rustica" and "Sinfonia sacra," are precursors of a later, darker style in which the idea of "metamorphosis" -- themes that evolve through subtle tonic and thematic relationships -- is reminiscent of Hindemith, and at times, even Wagner.
International attention came when his Fifth Symphony was performed at the International Society for Contemporary Music Festival in Copenhagen in 1947, after which Holmboe received commissions in various parts of Europe. The seventh and ninth symphonies are the most intense of Holmboe's orchestral output, and the Fourth Quartet the most intimate of his chamber works.
In some sense, Holmboe is more "main-line" than his Scandinavian contemporaries are. After his marriage in 1931 to the pianist Meta Graf, he traveled to her homeland, Romania, to collect folk tunes, and later to the Faeroe Islands on a similar quest though, except in the Rustic Symphony, folk elements are not prominent in Holmboe's major works. It remains for Holmboe to receive the consistent programming and advocacy that brought Sibelius to prominence in the '50s, and Nielsen in the '60s.