Long was a pupil of Antoine François Marmontel and at the Conservatoire de Paris by Henri Fissot. From 1906 to 1940 she taught at the Conservatoire, since 1921 also at the École Normale de Musique. Her pupils included Philippe Entremont, Jacques Février, Samson François and Ingrid Haebler. In 1942 she founded with Jacques Thibaud in Paris a music school; In 1943 she founded with Thibaud the prestigious international Long - Thibaud Competition ( Concours International Marguerite Long - Jacques Thibaud ) for pianists and violinists. Into old age, she had many private students.
Marguerite Long considered the most important French pianist of the 20th century. She was friends with Claude Debussy, Gabriel Fauré and Maurice Ravel and played inter alia, the premiere of Ravel's Piano Concerto in G major, which is also dedicated to her as well as his Le Tombeau de Couperin.
- Le Piano. 1959
- Au piano avec Debussy. 1960
- La Petite Méthode de piano. 1963
- Au piano avec Fauré. 1963
- Au piano avec Ravel. 1971