A Sydney marijuana activist has escaped a serious penalty for smoking a joint on the steps of Town Hall last month.

Jesse Willesee, who was supported in Downing Centre Local Court by his veteran TV journalist father Terry Willesee, pleaded guilty this morning to a charge of administering a prohibited drug.

Deputy Chief Magistrate Chris O'Brien sentenced Willesee to a 15 month good behaviour bond in relation to his 4-20 Day protest on April 20 .

Willesee, who believes marijuana has been instrumental in treating his ADHD, said he took a stand because he was fed up with being treated like a criminal for something he did not believe was a criminal act.

He was promptly arrested for his public demonstration after promoting his protest on social media.

His actions attracted publicity across the country and support from the NSW Greens who tweeted that he had "re-opened the debate" on marijuana reform.

Willesee was also supported by Dowson Turco Lawyers, who offered to represent him in court pro-bono in support of the protest to decriminalise drugs.

Speaking to ninemsn following the sentencing, Dowson Turco partner Nicholas Stewart said his client benefited from the court's discretion not to record a conviction.

"While Magistrate O'Brien rightly pointed to the aspect of Jesse's 'defiance', he also took into account the fact that such boldness should not aggravate the actual offence and warrant a conviction and criminal record. This was also in the context of medical marijuana, not bringing about another Woodstock," Mr Stewart said, adding it was the firm's belief that Australian drug laws should change.

"Drug use is a social issue, not a criminal one. We believe public funds are better spent on drug education and health rather than expensive criminal enforcement."