Born in the Paris region in 1975, Patrick Loiseleur began studying music at the age of five with the viola. He taught himself to compose from adolescence onwards. After completing a scientific baccalaureate, he gave in to his other great passion by studying mathematics. He entered the École Normale Supérieure in Paris and earned a PhD in computer science from the Université Paris-Sud – Orsay. In 2007, he returned to formal music studies at the ENM Alfred Cortot (with Michel Merlet), where he obtained a Diploma in Composition and Orchestration in 2009, then at the Conservatoire Royal de Liège, where he earned a Bachelor's degree in Viola in the class of Pierre-Henri Xuereb in 2011, and a Master's degree in Composition in the class of Michel Fourgon in 2013. He currently divides his time between a part-time position as a research engineer and musical composition.

In 2013, his Victoire de Guernica for coloratura soprano and instrumental ensemble was awarded a prize at the Rencontres internationales de composition de Cergy-Pontoise. In 2014, his piece for 13 violas, "13.2 Billion Light-Years", was premiered at the Cologne Philharmonie by Vincent Royer and the viola section of the Gürzenich Orchestra. In 2019, baritone L'Oiseleur des Longchamps and pianist Mary Olivon released a disc of his songs on the Triton label, entitled Aporie. Another album, En Blanc et Noir, with Orlando Bass (piano), Philippe Hattat (piano) and Rachel Koblyako (violin) was released in 2020. During the Covid-19 pandemic, he wrote his first opera, Papageno et Tindarella, which was partially premiered in the summer of 2023.

He collaborates with artists such as Vincent Royer (viola), Sevan Manoukian (soprano), Pascal Devoyon and Rikako Murata (piano), Jean-Pierre Peuvion (clarinet), Christophe Beau (cello), Karine Lethiec (viola), Axia Marinescu (piano), and Alain Pire (trombone).

His original style stems as much from his unconventional background as from a genuine independence of spirit. He does not seek to win competitions or commissions, but above all to express contrasting emotions with sincerity. He nevertheless remains influenced by French music from Ravel to Messiaen, Grisey and Murail. His music, always respectful of performers and voices, is characterized by great freedom, by stylistic ruptures and blends, and by a sense of theatre perceptible even in purely instrumental works.

He has developed his own harmonic theory under the name of hypertonal music, which aims to transcend the binary opposition between tonality and atonality, between tradition and the avant-garde. This involves working with chords of 6, 7, or 8 notes, with slightly saturated colors, in which a tonal center remains perceptible. Tonal functions are then completely rethought within an expanded space that encompasses both tonality and serialism. On one side, by lightening the textures toward 4- or 5-note chords approaching the 7ths and 9ths of tonal music; on the other, by intensifying the dissonances or saturating all the way to the cluster.

He also writes the Journal de Papageno, a blog (in French) where, since 2007, he has been sharing his favorites as well as his thoughts on his work and contemporary music.

Committed to children's rights advocacy with the organization Face à l'Inceste since 2016, he has authored or co-authored three practical books (in French) dedicated to preventing child sexual abuse: