Ernest Fanelli (29 June 1860 – 24 November 1917) was a French composer who is known for his works which have been considered as precursing Impressionism. He gained renown when his symphonic poem Thèbes premiered in Paris; this was a work incorporating elements associated with music ahead of its time, such as unique harmonies, extended chords, and polytonality.

Fanelli was born in Paris to Italian parents and started studying music at the age of 10. He earned a living playing timpani and piano, eventually composing seriously when he was 22, although he abandoned the activity in 1894. Upon applying to work as a copyist for Gabriel Pierné in 1912, his music—a manuscript of Thèbes, composed in 1883—astonished the latter, and a performance led to wide publicity and critical assessment of Fanelli's music and of the roots of the Impressionist style, especially that of Claude Debussy. Fanelli lived in poverty and struggled to support his family. He died in 1917 in Paris.

His oeuvre includes orchestral works, 32 orchestrally-accompanied songs, a few chamber works and a three-act opera buffa. Most of his works are of long duration, which may have discouraged their performance, as may their modernism. Dark humor is a common theme in some compositions, and he often used full orchestras with a large brass section. George Antheil asserted that Fanelli was "one of the greatest inventors and musical iconclasts of all time" but bemoaned that he "discovered the nuclei of a new movement, but he failed to discover that movement itself".