While still studying at the conservatory, Fleury played in the orchestras of the Folies-Bergere and the Folies Dramatique. Later he played with the Association des Grands Concerts, led by Reynaldo Hahn, Concerts Berlioz, conducted by Pierre Monteaux, and the Concerts Cortot. But his interest shifted from orchestra participation to solo and small ensemble performances. In 1902 Fleury joined Barrère's chamber ensemble, (SMIV), as second flute. By 1903 Fleury was touring as a soloist throughout Europe. He was particularly popular in England, where he appeared in over forty concerts between 1905 and 1925, the first on 16 October 1905 with
Dame Nellie Melba. He made his first visit to the United States with soprano
Emma Calvé on her 45-city tour in 1905–06. He provided
obbligato accompaniment for Calvé's solos (as he had for Melba) and performed works by Handel and Mozart with other members of the touring company. In 1905 Fleury assumed leadership of the SMIV when Barrère left to take a position with the
New York Symphony Orchestra. The following year he founded the Société de Concerts d'autrefois, an ensemble dedicated to performing music of the 17th and 18th centuries on
period instruments. (Although Fleury continued to play his Boehm instrument rather than a
baroque flute.) Fleury's most well-known performance occurred on 1 December 1913. Claude Debussy had composed a piece for unaccompanied flute as incidental music for the third act of
Gabriel Mourey's play,
Psyché. At the premiere of the play, held in the music salon of arts patron Louis Mors, Fleury played, from offstage,
La Flûte de Pan. Reviews of the music were positive. Critic Georges Casella wrote in
Comœdia: Another critic wrote: Fleury kept the manuscript to himself; no one else performed the piece during his lifetime. Re-titled
Syrinx, it was published in 1927, after Fleury's death, and became recognized as the seminal flute solo of the twentieth century. Fleury's concert career was interrupted by
World War I. After entering the army, he became part of
Fernand Halphen's first military orchestra (August 1914 – December 1915), which performed for the troops and for the local populace. Halphen, who had also studied at the Paris Conservatory, added selections of classical music to the standard repertoire of marches, dances and patriotic songs, which gave Fleury opportunities for solos. The orchestra disbanded when the soldier-musicians were reassigned to other units. After the war, Fleury returned to touring and writing, promoting Baroque music along with contemporary French music. By 1924, the SMIV had premiered "no less than
one hundred and twenty-five works [...] and revived all the classical or modern works of any importance." Danielle Gaudry, writing about the history of early chamber wind ensembles, notes: "At this point, it seemed that virtually every major French composer in succeeding generations would be interested in contributing something to the growing repertoire of chamber wind music." ==Writing and editing==