Born in Paris on October 14, 2004, Kassoum Ouattara started playing football very early, joining US Ivry at the age of seven. He then moved to FC Montrouge 92 in 2017, before joining the professional club Amiens in 2020. The left back thus completed his training there and made his first start in Ligue 2 in August 2022 against SC Bastia. He was then only 17 years and 310 days old. He played a total of 11 matches during that season then became the starter at the start of the following year where he was able to participate in 10 matches, all of them in the starting XI. With strong performances and good quality in his crossing, he also became a part of the youth setup for the French Youth Teams (2 with the U18s, 3 for the U19s and one with the U20s), alongside other Monegasques like Edan Diop, Eliesse Ben Seghir or Malamine Efekele. Kassoum joined AS Monaco in November 2023 on a five year contract.