Wrestling in the Greco-Roman lightweight class most of his career, Kyösti Lehtonen won Olympic gold in 1956 and World Championship silver in 1953 and 1955. He also competed at the 1960 and 1964 Olympics and 1958 and 1962 World Championships, but did not medal, with his best finish in those tournaments being fifth at the 1960 Olympics. Lehtonen also won nine Finnish titles during his career: in 1952-57, 1960 and 1962 in Greco-Roman lightweight and in 1961 in Greco-Roman welterweight. Lehtonen finished his sporting career after the 1964 Olympics and later worked as a wrestling coach. After coaching the Norwegian national team for half of a year, and then coaching the Danish national team for another half of a year, Lehtonen returned to Finland and was the coach of Helsingin Paini-Miehet from 1965-67. From 1971-74 Lehtonen was head coach of the Finnish national team and was later a board member of Finnish Wrestling Federation.