Lehtonen made her international debut on March 2, 2017, during the 2016/17 IBU Cup season at a competition held in Kontiolahti, Finland.

Lehtonen achieved her first World Cup top-10 finish in early January 2018 in Oberhof, as part of the Finnish women's relay team.

Competing alongside Kaisa Mäkäräinen, Mari Laukkanen, and Laura Toivanen, she helped secure a 7th-place finish, marking the best result for a Finnish women’s relay team since the 6th place at the 2003 Biathlon World Championships.

She competed in the sprint event, finishing 79th, and was part of the Finnish women's relay team that secured 15th place.

In December 2024, Lehtonen achieved a career-best performance by finishing 7th in the pursuit event at the Biathlon World Cup in Annecy, France.