Thon became Norwegian orienteering champion in relay with IF Sturla seven years in a row, in 1979, 1980, 1981, 1982, 1983, 1984, and 1985.

[2][3] He was awarded Bjarne Bjerckes pokal for his results in the long distance national championships.

[5] Thon competed at the 1981 World Orienteering Championships in Thun, Switzerland, where he placed 10th in the individual competition, and won a gold medal in the relay event, together with Øyvin Thon, Tore Sagvolden and Sigurd Dæhli.

He passed the leader when the Swiss runner had a miss at the tenth control,[8] and won the relay with a margin of one and a half minute ahead of the Czechoslovak team.

[10] He was an older brother of Øyvin Thon, a seven-times world champion in orienteering.