Career
He competed at the 1920 Olympics in the pentathlon, long jump and decathlon and at the 1924 Olympics in the pentathlon and 4 × 400 m relay. He retired after learning that pentathlon was excluded from the 1928 Olympics. At the 1920 Olympics he tried decathlon, but gave up after five events.
He semi-retired after the Olympics, but returned in 1922, again winning the national long jump and pentathlon titles.
In 1984, Lehtonen a bronze statue of Lehtonen was installed at the sports park in Mikkeli, his home town.