Cosnefroy was born into a family passionate about cycling. His grandfather was the organizer of a race in the English Channel, while his father often took him to see bike races during his youth. He first started competing at the age of 8 with the Union Concorde Bricquebetaise.[5] In 2011, he joined the Pôle Espoir de Caen, where he stayed for three years.[6] He took his first victory at the age of 16 in the Prix Louis-Cosnefroy, a race held as a tribute to his great-great-grandfather Louis Cosnefroy.[7] However, during his years in the junior category, Cosnefroy saw little success. In 2014, he moved up to the under-23 category, joining team Bricquebec Cotentin. The following year he joined Chambéry CF [fr], the development team of AG2R La Mondiale after hitchhiking along the nine-hour drive to apply.[8] This year, he achieved modest success in amateur and under-23 races. In 2016, he began to obtain more results, notably placing second by half a wheel length to Valentin Madouas at the national amateur road race championships, and second to Paul Ourselin in the under-23 national championship.[9][10] He joined AG2R La Mondiale as a stagiaire in August, placing 4th in the road race at the UEC European Under-23 Road Championships.[11]
The 2017 season was a major turning point in Cosnefory's career, and was his final year competing as an amateur. He took his first elite category win in May: stage 2 of the Rhône-Alpes Isère Tour, holding off the peloton for almost 160 kilometers.[12] The same month, he placed sixth in the Grand Prix de Plumelec-Morbihan, his first top ten in a 1.1 or higher category race.
Cosnefroy started 2024 on strong form, winning stage 2 and the overall title of the Tour des Alpes-Maritimes in February, followed up with a sixth place finish at Strade Bianche in early March.[21] Three weeks later he won Paris–Camembert, followed by his first win at the Brabantse Pijl after having been on the podium three times before.[22] In early May, he won the Grand Prix du Morbihan.
Major results
2016
2nd Road race, National Under-23 Road Championships
2nd Road race, National Amateur Road Championships