He is married to Brit Volden, also a World Orienteering Champion.

[2] Thon won gold medals at the 1979[3] and 1981 Individual World Orienteering Championships,[4][5] and finished second in 1983.

[6] He is also five times Relay champion, as a member of the Norwegian winning teams in 1981 (Thun, Switzerland),[5] 1983 (Zalaegerszeg, Hungary),[6] 1985 (Bendigo, Australia),[7] 1987 (Gérardmer, France) and 1989 (Skaraborg, Sweden).

[8] He won the Overall World Cup in Orienteering in 1988, and finished second in 1986.

[9] He won the relay with the club IF Sturla seven years in a row from 1979 to 1985.