Helen Clark has been appointed to the Global Commission on Drug Policy, an independent body advocating for reducing the harm caused by drugs.
Ms Clark joins world leaders such as Kofi Annan, Ruth Dreifuss, the former President of Switzerland and Caesar Gaviria, the former President of Colombia.
The NZ Drug Foundation's Ross Bell says the appointment is very welcome.
"It's likely New Zealand will find ways to involve her in the domestic discussions we will soon be having about health approaches to drugs and cannabis law reform."
Mr Bell says the former Prime Minister will "throw her weight behind global efforts to drop punitive approaches to drugs in favour of putting health first".
Ms Clark tweeted she is "pleased to join Global Commission on Drug Policy & its advocacy for evidence-based approaches.
"Proud of work @Mandeep_Dh [Mandeep Dhaliwal - Director for the UNDP's Health and Development Group] & #UNDP health/HIV team did on these issues when I was Administrator."