The Société des compositeurs de musique (SCM), the less avant-garde of French organizations promoting new music,[a] awarded his quintet for piano and winds first prize in 1901 and premiered it on 28 February of that year.

[2] He won the Prix de Rome in 1901, composing in a conventional style to please the judges, while Maurice Ravel showed his contempt for the assigned text.

[b] Caplet's native city celebrated his participation with a performance of his Été for chorus and orchestra (1899) on 3 April 1901 and marked his victory by presenting several of his works at a concert on 24 November, including L'Été, Pâques citadines for chorus and orchestra, Feuillets d'album for flute and piano (1901), and the cantata that won him the Prix de Rome, Myrra (1901).

[1] Until the end of 1905, Caplet lived at the French Academy in Rome with the financial support the prize provided, though he took leave for long periods to attend performances in Berlin, Dresden, Hamburg.

[d] He secured the appointment through one of its co-founders, the impresario Henry Russell, whose wife Nina became a friend of Caplet during his time in Rome.

Works by Debussy that he led include L'enfant prodigue, the Children's Corner, Pelléas et Mélisande, and the incidental music to Le Martyre de saint Sébastien.

[1][e] At the end of 1914, after he had completed two movements of a work that became Les Prières, Caplet enlisted[9] in the French army and saw combat in the trenches at Verdun.

In 1917 he completed the third movement and the work premiered that same year in the small church of Ham, Picardy, accompanied by the distant sounds of artillery.

His Messe à trois voix for a capella female chorus had its premiere in Sainte Chapelle on 13 June 1922.

[16] In 1925, Caplet caught a cold and, given how his lungs had been weakened when he was gassed during his military service, developed pleurisy, which proved fatal.