Simon Thirsk (born 15 May 1977 in Cape Town) is a retired South African swimmer, who specialised in backstroke events.

In the 100 m backstroke, he fought off a challenge from Japan's Keitaro Konnai to power home with South Africa's first ever gold in 55.97.

[5] After winning a gold medal from the University Games, his entry time of 55.97 was officially accredited under a FINA A-standard.

[3][6] In the 100 m backstroke, Thirsk challenged seven other swimmers in heat six, including Cuba's Olympic silver medalist Rodolfo Falcón and Australia's overwhelming favourite Matt Welsh.

Leading off a backstroke leg in heat two, Thirsk recorded a split of 56.88, but the South Africans finished the race in fourth place and thirteenth overall with a final time of 3:42.44.