He is a former graduate of the Clairefontaine academy. After his departure from the academy, Isimat-Mirin joined Rennes and spent two seasons at the club before transferring to Valenciennes in 2009. He spent the 2009–10 season playing on the club's Championnat de France amateur 2 team. In September 2010, he was promoted to the first team by manager Philippe Montanier. Isimat-Mirin made his professional debut on 21 September in a Coupe de la Ligue match against Nîmes Olympique appearing as a substitute. Valenciennes won the match 5–4 on penalties. On 19 October, Isimat-Mirin signed his first professional contract agreeing to a three-year deal until July 2014. On 1 September 2014, it was announced that Isimat-Mirin was sent on loan to PSV Eindhoven until the end of the season.