Nicholas Cowdery SC - who was formerly responsible for leading the prosecution of drug dealers in the nation's largest legal system - has argued the criminal justice framework is ill-equipped to deal with drug use.
People who "feel the need to take mood-altering substances" should be able to do so, he told a landmark New South Wales parliamentary inquiry into the impact of cannabis regulation on Thursday.
"A person's choice to use a mood-altering substance without harming others must be respected as a human right," the former NSW Director of Public Prosecutions said.
If the purpose of the criminal justice system was to make the community safe, then it was "totally unsuited" to dealing with somebody who chose to use drugs, he said.
Mr Cowdery, former president of the NSW Council for Civil Liberties, noted "far more harmful" drugs such as alcohol and nicotine were legal and regulated.
"What right could the state tell me that I can't have a glass of wine with dinner?" he said.
"I have seen in my career the effects of alcohol time and time and time again and I've seen the statistics on the number of people who die from nicotine use.
"Cannabis doesn't do that."
Decriminalising cannabis for personal purposes would enable better government oversight of its use and the market, and free up law enforcement to look into more important criminal conduct, he said.
Mr Cowdery pointed to the "enormous success" of Portugal's drug decriminalisation strategy, in which those caught with small quantities are brought before a committee of medical and legal professionals.
"It has not led to increased drug use in Portugal ... in fact, it's reduced," he said.
"It has not had a honey-pot effect."
Inquiry chair and Legalise Cannabis MP Jeremy Buckingham said evidence from the US, Canada and Germany - parts of which had moved to decriminalise cannabis - pointed to the broad benefits of legal use.
"Legalisation is just common sense," he told AAP.
"It's going to save taxpayers billions of dollars, it's going to stop billions of dollars going into organised crime and it's going to lead to better health outcomes.
"It's just a matter of time .... it's about how we do it, not if."
But Premier Chris Minns said he would stand by an election promise not to change laws that criminalised cannabis use outside of medicinal settings.
"I'm not going to break an election commitment," he said.
The state Labor government previously introduced relaxed drug laws that allowed people caught with small amounts of certain illicit substances to be spared court appearances and instead fined or diverted to counselling.
A long-standing cannabis caution scheme also applies in NSW for people found with minor amounts but is applied at police discretion.
The ACT is the only Australian jurisdiction to have decriminalised cannabis possession for personal recreational use.
NSW will hold a drug summit in October and December - another Labor commitment - when MPs and experts will consider the legalisation of cannabis, the use of pill-testing sites and other harm-reduction measures.
