After appearing in the late 1980s and early 1990s on an Australian television series titled The Comedy Company, Rowsthorn starred in the children's program The Gift. He is perhaps best known, however, for his television comedy roles as Brett Craig and Warren Cronkshonk on, respectively, Kath & Kim and Let the Blood Run Free.
Before beginning his entertainment career, he received his teaching degree from Rusden College in Victoria, Australia.
In the early 1980s, he performed with a music and comedy group called The Cactus Brothers.
His marriage to Gabrielle Rowsthorn resulted in four children. His brother, business executive Mark Rowsthorn, became one of the wealthiest men in Australia.
In a 2005 made-for-TV film titled Little Oberon and starring Sigrid Thornton, Rowsthorn played the humorous character of "Miss Kafka."