De Wet started his first-class career with the Titans in 2000-01 while studying at the University of Technology in Pretoria and he also played for the UCBSA National Academy. He moved back to Rustenburg and played the following two seasons for the North West amateur team before being signed by the Lions in 2005-06. He rewarded them with 42 wickets at 18.47 and in 2006-07 grabbed 61 at 20.21, including six five-wicket hauls, finishing as the clear leading wicket-taker in domestic cricket. He was rewarded with a place on the South Africa A tour of India at the start of 2007-08 and was signed by Middlesex as a Kolpak player for the 2008 season, before earning an unexpected call-up to South Africa's Test squad for the visit of England in December 2009.