After acting as a child between the ages of seven and twelve in more than fifteen films (most notably with the Piccolo Teatro di Milano under the direction of Giorgio Strehler and playing Mozart at the age of eight in Marcel Bluwal's TV film), Karol Beffa undertook general studies alongside his musical studies.

After graduating top of his class from the Ecole Normale Supérieure, he went on to study history (BA), English (MA), philosophy (MA at Cambridge University) and mathematics. He entered the Paris Conservatoire in 1988, where he won eight First Prizes (harmony, counterpoint, fugue, 20th-century music, orchestration, analysis, vocal accompaniment and piano improvisation). After passing the agrégation in music, he taught at the Université Paris IV-Sorbonne (1998-2003). In 2003, he obtained a doctorate in musicology with a thesis on Ligeti's Etudes pour piano. Since 2004, he has been a lecturer at the Ecole Normale Supérieure. In 2012-2013, he was elected to the annual chair of artistic creation at the Collège de France, and in 2015 he defended an Habilitation to direct research.

In 2000, he was selected to represent France at the International Biennial of Young Artists in Turin. In 2002, he was the youngest French composer to be programmed at the Présences festival. Composer in residence with the Orchestre National du Capitole de Toulouse from 2006 to 2009, he composed a violin concerto premiered by Renaud Capuçon. As a pianist, he regularly accompanies silent films, readings and improvises on themes suggested by the audience. As a composer, he has written some twenty film scores and three stage scores. In 2016 he was awarded the Grand Prix lycéen des compositeurs and in 2017 the Grand Prix de la musique symphonique de la SACEM for his entire career. In 2013 and 2018, he won the Victoires de la Musique classique awards.

In 2015, he published (with Cédric Villani, Flammarion) Les Coulisses de la création and, in 2016, György Ligeti (Fayard). In 2017: Parler, Composer, Jouer. Sept leçons sur la musique (Seuil). In 2018: Diabolus in opéra. Composing with the voice (Alma) and Anagrammes à quatre mains. Une histoire vagabonde des musiciens et de leurs œuvres (with Jacques Perry-Salkow, Actes Sud). In 2019: Ravel. Un imaginaire musical (with Aleksi Cavaillez and Guillaume Métayer, Seuil-Delcourt). In 2021: Saint-Saëns au fil de la plume (Premières Loges). In 2022: L'Autre XXe Siècle musical (Buchet-Chastel) and, with Guillaume Métayer, Le Mystérieux Boléro. Sol et Rémi with Ravel and Le Bal au clair de lune. Sol et Rémi with Beethoven. In 2023: Camille Benoit, composer (La Rumeur libre) and, with Guillaume Métayer, Le Mystérieux Boléro. Sol et Rémi avec Satie (Seghers). In 2024: Bernard Herrmann (Actes Sud). Latest monographic CDs released: Into the Dark (Aparte), Blow up, En blanc et noir, De l'autre côté du miroir (Indesens), Douze Etudes (AdVitam), Talisman (Klarthe), Media Vita and Galerie des glaces (Klarthe).