A Sydney medical marijuana activist has been arrested after blazing up on the steps of Town Hall.

Jesse Willesee, the son of veteran TV journalist Terry Willesee and nephew of Mike Willesee, announced his plans to take part in the pro-pot protest known as 420 Day by posting a photo of himself smoking a joint outside the Opera House on Instagram to more than 6600 followers.

"I'm willing to stand up for what I believe in and if that means the police turn up, that is something I will have to regretfully but peacefully accept," the 27-year-old self-styled conceptual artist told ninemsn, adding that Australia is stuck in the dark ages on the issue.

Mr Willesee said he had never had a run-in with the law but it would "be stupid not to think that there won't be a police presence", adding that the nearest station was only 100m away.

He was arrested at 4.21pm - one minute after lighting up - and charged with administering a prohibited substance. He will appear in court in one to two weeks.

Jesse Willesee was arrested at 4.21pm, just one minute after he dared to light a joint on the steps of Sydney Town Hall. (Supplied)

Come rain, hail or shine ... the self-styled conceptual artist was determined to make a point. (Supplied)

The protest comes one day after the Queensland and Victorian state governments joined forces with NSW to take part in medicinal cannabis clinical trials.

Mr Willesee, whose recently launched a fashion line and had his artwork published by the Huffington Post , has used medical marijuana to treat his chronic symptoms of ADD and ADHS since the age of 23, and credits the drug with changing his life.

The Surry Hills resident described as "traumatic" his school years on prescribed drug Ritalin, which helped him to concentrate but disrupted his sleep and curbed his hunger.

Mr Willesee joins conservative Coalition Senator Barry O'Sullivan and Lucy Haslam, the mother of late medical marijuana campaigner Dan Haslam, who have criticised Australian governments for moving too slowly to provide sick people with access to the drug.

He said everyday Australians were risking prosecution to obtain cannabis for their loved ones. Because cannabis was illegal they did not have any assurance of quality and were forced into contact with "dealers" to obtain it.

Jesse Willesee smoked marijuana outside Parliament House in Sydney last year as part of a 420 Day pro-weed protest. (Supplied)

He also posed in front of six Sydney police stations last year as part of his own controversial decriminalisation protest. (Supplied)

"There are a lot of people in Australia who know these laws are out of touch, but the government doesn't want to listen," Mr Willesee said.

Inspired by the decriminalisation of medical marijuana in Los Angeles, he said it didn't take a "stoner" to understand the laws in Australia were extreme and outdated.

Mr Willesee said his father, Terry, would prefer he did not smoke, but was supportive of his right to stand up for what he believed in.