Along with Camille Saint-Saëns, Casadesus founded the "Société des instruments anciens" in 1901. The society, which operated between 1901 and 1939, was a quintet of performers who used obsolete instruments such as the viola da gamba, or Casadesus's own instrument, the viola d'amore. The quintet was also notable in its day for premiering rediscovered works by long-dead composers. It was later discovered that Casadesus and his brothers, notably Marius Casadesus, wrote these works. The Adélaïde Concerto, allegedly by Wolfgang Amadeus Mozart, is sometimes mistakenly attributed to Henri but is actually by Marius. However, Henri is believed to have been the author of a "Concerto in D Major for viola" ascribed to Carl Philipp Emanuel Bach, described by Rachel W. Wade in her survey The Keyboard Concertos of Carl Philipp Emanuel Bach. This concerto appeared in 1911 in a Russian edition, allegedly "transcribed...for small orchestra by Maximilian Steinberg," and was subsequently performed by conductors such as Darius Milhaud and Serge Koussevitsky, then recorded by both Felix Prohaska and Eugene Ormandy, all under the false attribution. "Thus," Wade wrote in 1981, "at the present time, the most frequently recorded concerto of C.P.E. Bach is a spurious one." Henri is also credited with the "Handel Concerto" and the "J.C. Bach Concerto," which are both for viola as well. These are often referred to as "The Handel/Casadesus Concerto" and "The J.C. Bach/Casadesus Concerto". Scholarly criticism has confirmed that both these concerti were written by Henri Casadesus in the style of their purported composers. Casadesus is also the composer of a violin concerto in D major in the style of Boccherini.
Le rosier, Opera buffa in 3 acts ; libretto by Maurice Devilliers
Les plaisirs champêtres, ou, Les tentations de las bergère et l'amour vainqueur, Ballet in 1 act ; music derived from Plaisirs champêtres and Divertissement by Michel Pignolet de Montéclair
Cotillon III, Opera buffa in 3 acts ; libretto by Gabriel Alphaud and Pierre Maudru
Valses de France, Fantasie musicale et grand spectacle "Sur des airs célèbres de Gounod, G. Bizet, B. Godard, L. Delibes, Hervé, O. Métra, Lacome, P. Delmet" in 2 acts, 18 scenes ; libretto by and Albert Willemetz
La petite-fille de madame Angot, Operetta
;Orchestral
Concerto in D major for small orchestra ; original "for four viols concertante"; falsely attributed to Carl Philipp Emanuel Bach
Concerto in D major for violin or viola and piano or orchestra ; original "for four viols concertante"; falsely attributed to Carl Philipp Emanuel Bach