Halvarsson, who started for the Föllinge IK and the Hammerdals IF , had his first international success at the 1968 Winter Olympics in Grenoble . There he won the silver medal with the relay. He also took 12th place over 30 km, seventh place over 50 km and fifth place over 15 km. At the Nordic World Ski Championships in 1970 in Štrbské Pleso , he won the silver medal with the relay. In the same year he was third in the Wasalauf . In 1968 he won the Swedish championships over 50 km. He was also champion in 1965 and 1967 with the season of Föllinge IK and in 1969 with the season of Hammerdals IF.