| Party: | African National Congress |
| Office1: | Member of the National Assembly |
| Termstart1: | 1995 |
| Termend1: | 1999 |
| Citizenship: | South Africa |
| Birth Date: | 4 March 1953 |
| Birth Name: | Marius Oliver Robertsen |
| Office: | Delegate to the National Council of Provinces |
| Termstart: | April 2004 |
| Termend: | May 2009 |
| Constituency Am: | Eastern Cape |
Marius Oliver Robertsen (born 4 March 1953)[1] is a South African politician from the Eastern Cape. He represented the African National Congress (ANC) in the National Assembly from 1995 to 1999 and in the National Council of Provinces from 2004 to 2009.
Though not initially elected in the 1994 general election,[2] Robertsen joined the National Assembly in 1995, filling a casual vacancy.[3] In the 1999 general election, he stood for election as a candidate for the opposition New National Party (NNP), but he was ranked seventh on the NNP's party list for the Eastern Cape and did not gain a seat. In the next general election in 2004, he returned to the ANC, which elected him to one of its seats in the Eastern Cape caucus of the National Council of Provinces.[4] He served a single term there.