Helen Clark will join other former heads of state on the prestigious Global Commission on Drug Policy.
The former prime minister will be working alongside former United Nations secretary general Kofi Annan, and prominent business people and cultural leaders such as Sir Richard Branson.
The commission is one of the world's leading think tanks on reducing drug harm on society.
She becomes the 25th member of the independent body advocating for evidence based drug law reform.
Clark today said she hoped to shift the focus of policy away from substances and onto harm-reduction and people.
"I believe that drug policy needs to evolve from a substance-based to a people-centred approach," Clark said in a statement.
"Harm reduction, prevention, and evidence-based treatment have shown their effectiveness around the world. I have witnessed this from New Zealand to Belarus. Now is the time to address the policy barriers to better outcomes. This is what I plan to work on with my fellow Global Commissioners."
Commission chair and former Brazilian President Fernando Henrique Cardoso was thrilled with the new appointments of Clark and former Prime Minister and President of Timor-Leste José Ramos Horta.
"I cannot understate my gratitude and satisfaction to see Helen Clark and José Ramos Horta join us from the Asia-Pacific region, highlighting how all regions of the world have leaders willing to move towards drug policy reform."
The NZ Drug Foundation was quick to congratulate Clark on her appointment, saying that she oversaw a sea-change of views on drug policy while at the UNDP.
"Having Helen Clark join this select group of global leaders is a real coup. The commission has become well known for championing cutting edge, health-focused approaches to drug problems," said foundation executive director Ross Bell.
"At the UN's general assembly meeting on the world drugs problem in April 2016, the UNDP strongly criticised current international drug policy, highlighting the disastrous costs it is producing particularly for the world's poor."
Clark said in 2013 the issue of drugs should be treated as a health issue, not as a criminal issue - a stance that the current Labour-led Government has taken.
Established in 2011 and now comprising 25 members, including 12 former heads of state and former UN secretary general Kofi Annan, the commission has been a champion for drug policy reform while also looking at issues such as public health, social integration, and human rights.
Clark was New Zealand's Prime Minister from 1999 to 2008 and head of the UN Development Programme from 2009 to 2017.