With two World Championship gold medals in singles and five more with the dominant in the 1980s, the Norwegian team relay competition Thon is one of the best orienteer of the decade.
His first gold medal won Thon 1979 at the World Championships in Tampere. As a freshman, he sent the defending champion and compatriot Egil Johansen with 1:10 minutes on the second rank. The Norwegian World Championship season of 1979, in the clay also marched with, but surprisingly only reached the sixth place. His second individual gold medal won Thon 1981 at the World Championships in the Swiss Thun. With almost two and a half minutes ahead, he pointed his compatriot gates Sagvolden in second place. The third Norwegian Morten Berglia came in third place. 1983 had to settle for second place behind Morten Berglia Thon. With the season he won his fourth overall gold at the World Championships. In 1985, he won gold in the relay again and reached in single seventh. At the World Championships 1987 in Gerardmer, he was re- seventh. 1989 Thon went in Swedish Skaraborg one last time at the World Championships at the start and won with the Norwegian team relay competition his seventh world championship gold medal.
In 1981 he was honored with the Morgenbladet gold medal.
In addition to his seven world titles Thon was seven times Norwegian champion: 1980 on the classic distance, and in 1981, 1983 and 1986 on the long distance. 1981, 1982 and 1984, he became Norwegian champion in night - orienteering.