Mouthon competed at the first Olympic triathlon at the 2000 Summer Olympics. She took seventh place with a total time of 2:02:53.41. Her split times were 19:48.98 for the swim, 1:05:28.50 for the cycling, and 0:37:35.93 for the run.
Her twin sister, Béatrice Mouthon, also competed in the 2000 Olympic triathlon.
- Evans, Hilary; Gjerde, Arild; Heijmans, Jeroen; Mallon, Bill; et al. "Isabelle Mouthon-Michellys". Olympics at Sports-Reference.com. Sports Reference LLC. Archived from the original on 2012-10-22.