Cassignol made her debut at the 2017 World Aquatics Championships in Budapest, and won a gold medal in the team relay.

[2][3] At the 2020 European Aquatics Championships held in 2021 due to the COVID-19 pandemic, she won a bronze medal in the 5 km open water event with a time of 58:51.4.

[4] In February 2024 she competed at the 2024 World Aquatics Championships in Doha, and finished in fifth place in the 5 km open water event and 16th place in the 10 km open water event.

With her results at the World Championships, she qualified to represent France at the 2024 Summer Olympics.

[5] She competed in the 10 km open water marathon and finished in seventh place with a time of 2:06:06.9.