[5] Having rode as a stagiaire for Omega Pharma–Quick-Step,[6] Sénéchal joined the team's development squad, Etixx–IHNed, for 2013,[7] where he won the Memoriał Henryka Łasaka one-day race,[8] before a stage win and successes in the general and points classifications at the Okolo Jižních Čech.

[12][13] He placed eighth overall at the Tour de Wallonie – winning the young rider classification[14] – and third at Dwars door het Hageland,[15] before making his first start at the Vuelta a España.

[19][20] He made his first start at the Giro d'Italia in May,[21] and following this, he took three further top-five finishes over the remainder of the season – fourth at the Brussels Cycling Classic,[22] third at the Grand Prix d'Isbergues,[23] and second to Sonny Colbrelli in the Gran Piemonte.

[42] In his first start of 2021, Sénéchal finished second to Giacomo Nizzolo in a bunch sprint at the Clásica de Almería, having not been earmarked as Deceuninck–Quick-Step's main sprinter for the race.

[44] The following week, he led home a small group for second place at the E3 Saxo Bank Classic behind teammate Kasper Asgreen,[45] who had attacked with 5 kilometres (3.1 miles) remaining.

[52] He then finished in third place at Dwars door het Hageland in June,[53] before taking his only victory of the season later the same month – when he won the French National Road Race Championships in Cholet, winning the sprint from a group of five riders.

[54] He made his début in the jersey at the Tour de France, riding the race for the first time since 2017, being called up late to replace Tim Declercq.

[62] His best result during the season was a tenth-place finish at the Antwerp Port Epic, having been set back by two collarbone fractures, the death of his grandfather and burnout which had left him contemplating his career in the sport.