| Intro | South African sprinter |
| Was |
Runner Athlete Sprinter |
| From | South Africa |
| Type | Sports |
| Gender | male |
| Birth | 13 May 1911, Standerton |
| Death |
30 June 1983 (aged 72 years) |
Marthinus Wilhelminus S. Theunissen (13 May 1911 – July 1983) was a South African athlete who competed in the 1936 Summer Olympics. He was born in Standerton.
In 1936 he was eliminated in the semi-finals of the 200 metres event and in the quarter-finals of the 100 metres competition. He was also a member of the South African team which was eliminated in the first round of the 4×100 metre relay contest. At the 1934 Empire Games he won the silver medal in the 100 yards event as well as in the 220 yards competition.