Le Mercier began learning to skate in 2003.[1] He skated with Jade Marchal for at least five seasons, winning the French national novice title in March 2015.[2]
Le Mercier teamed up with Loïcia Demougeot in 2015. The two made their international debut in February 2016 at the Bavarian Open. They debuted on the Junior Grand Prix series in August of the same year.
Demougeot/Le Mercier qualified to the final segment at the 2018 World Junior Championships in Sofia, Bulgaria. They ranked fourteenth in the short dance, fifteenth in the free dance, and fifteenth overall.
In February 2019, they won the French junior national title for the first time. They placed seventh in the rhythm dance, ninth in the free dance, and eighth overall at the 2019 World Junior Championships in Zagreb, Croatia.
Following the COVID-19 pandemic causing the cancellation of what would have been their final international junior season, Demougeot/Le Mercier moved up to the senior ranks for the 2021–22 season. They made their Challenger series debut at the 2021 Lombardia Trophy, finishing ninth.[5] Making their Grand Prix debut at the 2021 Internationaux de France, they finished ninth among ten teams.[6] After winning the bronze medal at their first senior French nationals, Demougeot/Le Mercier made their debut at the European Championships, finishing sixteenth.[7]
2022–23 season
Demougeot/Le Mercier began the 2022–23 season at the 2022 Lombardia Trophy, where they finished in fifth place. Given two Grand Prix assignments, they finished fourth at both the 2022 Skate America and the 2022 Grand Prix de France.[5] Speaking after the latter, an enthused Le Mercier said: "if someone would have told us before the Grand Prix season that we would end up with fourth place, we wouldn't have believed it."[8]
Demougeot and Le Mercier performing a lift during their free dance at the 2024 World Championships
2023–24 season
At the 2023 Budapest Trophy, Demougeot/Le Mercier won the bronze medal, their first on the Challenger series.[7] Given two Grand Prix assignments, they finished fifth at the 2023 Cup of China. They indicated they would remain in China until their second event, Japan's NHK Trophy.[9] After training at Beijing's Olympic center, they finished fifth at NHK Trophy as well. Demougeot called the extended absence from home "tough but so rewarding at the same time."[10]
Demougeot/Le Mercier won their second consecutive French national silver medal before competing at the 2024 European Championships in Kaunas, Lithuania. Only eighth in the rhythm dance, albeit with a new personal best, they rose to fifth overall with more new personal bests. Demougeot said "the score exceeded our expectations."[11] They went on to win a gold medal at the International Challenge Cup.[12]
At the 2024 World Championships in Montreal, Demougeot/Le Mercier finished eleventh in the rhythm dance with another new personal best score.[13] Thirteenth in the free dance, they remained eleventh overall.[14]
