On 11 August 2017, Larsonneur made his professional debut with Brest, keeping a clean sheet in a 0–0 Ligue 2 draw to Gazélec Ajaccio.[1]
On 12 July 2022, Larsonneur extended his contract with Brest until 2024 and was loaned to Ligue 2 side Valenciennes for the 2022–23 season, with the option to extend the loan for the 2023–24 season as well.[2] However, on 6 January 2023, his loan at Valenciennes was cut short; he signed for fellow Ligue 2 side Saint-Étienne on a permanent transfer for a fee of €1.6 million. Larsonneur signed a contract until 30 June 2025.[3]