 Playing mainly on the wing, Thiessen started his AFL career at Richmond in 1993, debuting in a 139-point loss to his future club , but was delisted after just one season.He spent the next four years with Norwood in the SANFL, playing in their 1997 premiership side and also winning a Fos Williams Medal that year for his performance for South Australia in an interstate match against the ACT.Thiessen was recruited by the Adelaide Crows for the 1998 season and played in their winning Grand Final that year against North Melbourne.