Opposition leader Daniel Andrews' pledge to decriminalise cannabis for treatment of life-threatening illnesses comes as support for legalisation of "medical marijuana" gains momentum in Australia and overseas.

In New South Wales, new legislation to legalise medical marijuana may pass as early as next month after both major parties indicated tentative support.

Tamworth MP Kevin Anderson plans to introduce a private member's bill in support of medical marijuana possibly at the next state parliamentary sitting in September. NSW Premier Mike Baird, Deputy Premier Andrew Stoner and opposition leader John Robertson have all given their provisional support for the bill.

At a federal level, a multi-party group of MPs – including northern Victorian Liberal MP Sharman Stone and Queensland MP Warren Entsch – are working on a bill to allow cannabis oil as a medical treatment for epilepsy sufferers, cancer patients and other life-threatening illnesses.

Mr Entsch said he opposed recreational marijuana use, but supported the use of cannabis as a prescribed treatment.