Andre du Plessis on Saturday said the aim was also to highlight the many uses of cannabis and stressed that the vast majority of the marchers were professionals and not beatniks or hippies.
Cannabis, or marijuana, is colloquially called "grass" in several countries.
"We will be discussing cannabis and its potential in South Africa's industrial sector, in agriculture and in health and from the criminal and police perspective."
Du Plessis, an information technology engineer, said he had undertaken a six-year study and found that it could be used in low-cost housing.
"My research shows that we can deliver a 82 sq metre house for 15,000 rand ($2,188) which is three times the size of a house which is being currently built using conventional methods.
"These houses can be built with bricks made out of the stalk of the hemp and mixed with lime and sand. The houses will be thermal with great insulation."
"But the most interesting information is that it can help in fighting cancer tumours ... and lead to remission in various parts of the body but most importantly in the brain."
"But the most interesting information is that it can help in fighting cancer tumours"
Andre du Plessis,
Du Plessis said there would be similar marches in other countries on Saturday, organised under the umbrella of three organisations - Million Marijuana March, Cannabis Culture and Cheers Not Wars.
He deplored the fact that Cape Town was the only city in Africa participating in the event.
"It's important that Africa catches up to the rest of the world. Agriculture is a very important sector here - we have the land, we have the farmers, we have the sunshine and we have the rain."
He slammed South African laws on cannabis as being muddled and almost "defunct".
He stressed there were few convictions for cannabis use anyway due to "overcrowded prisons" and called for its decriminalisation.
But he underlined that nobody would be allowed to smoke at the march, saying: "I don't want to start a civil disobedience movement on the streets."