Mahadi bin Haji Wasli is a Brunei diplomat who became the Deputy Secretary-General of ASEAN from 1994 to 1997, ambassador to Russia from 2001 to 2003, Vietnam from 2007 to 2013, and the permanent representative to the United Nations (UN) in Geneva from 2003 to 2007.
From 1994 to 1997, Mahadi held the position of Deputy Secretary-General of the Association of Southeast Asian Nations (ASEAN).
[2] From 1999 to 2001, he concurrently served as the permanent representative of Brunei to the United Nations in Geneva, and holding the title of non-resident ambassador to Switzerland.
[5] From 10 July 2007 to 29 August 2013, he extended his diplomatic service as the Brunei ambassador to Vietnam.
[8] Together with Mustappa Sirat, they attended the first ASEAN Defence Minister's Meeting – Plus (ADMM+) on 12 October 2010 in Hanoi.