Bonis was born to a Parisian lower-middle-class family and was educated according to the strict norms of the Catholic morality of the time. Of great talent and musical sensitivity, she taught herself the piano. Initially, her parents did not encourage her music, but when she was twelve, they were persuaded by a professor at the Conservatoire to allow her to receive formal music lessons. At the age of sixteen, she began her studies at the prestigious Conservatoire and attended the accompaniment, harmony and composition classes, where she shared the benches with Claude Debussy and Gabriel Pierné and received tuition from César Franck. Due to the difficulties encountered by women who wished to compose, she adopted the more neutral form of her first name "Mel". At the Conservatoire she met and fell in love with Amédée Landély Hettich, a student, poet, and singer, setting some of his poems to music. Unfortunately, her parents disapproved of the match, and in 1883 arranged for her to marry the businessman Albert Domange, 25 years her senior (and a widower with five children from his two previous marriages), after which for a period she disappeared into domesticity and had three children. For Bonis it was not an ideal marriage: Domange did not like music. In the 1890s she met Hettich again, who encouraged her to return to composition, after which her career took off. However she also began an affair with Hettich, which led to the birth of an illegitimate child, Madeleine. The child was put into the care of a former chambermaid, whilst Bonis devoted all her energies to composition, becoming a member of the Société des compositeurs de musique and a published composer with Éditions Alphonse Leduc.