Marguerite Long (13 November 1874 – 13 February 1966) was a French pianist and teacher.

Marguerite Marie-Charlotte Long was born in Nîmes. She studied with Henri Fissot at the Paris Conservatoire, taking a Premier prix in 1891, and privately with Antoine François Marmontel. From 1906 to 1940 she taught at the Paris Conservatoire, and in 1920 she succeeded Louis Diémer as professor of piano. She also taught privately.

Long's husband, Joseph de Marliave (1873–1914), was killed in August 1914 in action during World War I. Maurice Ravel dedicated the last section, the Toccata, of Le tombeau de Couperin to him. Marguerite Long gave the first performances of this work in 1919, and in January 1932 the premiere of Ravel's Piano Concerto in G major, which was dedicated to her, followed shortly by its first recording with Ravel conducting.

In 1943 she and violinist Jacques Thibaud established the Marguerite Long-Jacques Thibaud International Competition for violinists and pianists, which takes place each year in Paris. Since 2011, the competition has included singers and it is now known as the Long-Thibaud-Crespin Competition, in honour of the soprano Régine Crespin.

In June 1956, the French government sponsored a concert at the Sorbonne in honour of Long's contribution to French musical life. She herself, although now aged 81, played Gabriel Fauré's Ballade, Op. 19 with the Orchestre National de France under Charles Munch. The centrepiece was the first performance of a collaborative orchestral suite written in her honour by eight French composers, titled Variations sur le nom de Marguerite Long.

Marguerite Long died in Paris in 1966, aged 91.