Williams has assisted nearly two dozen states and sub-state entities in major international peace negotiations, legislation drafting and policy planning, and post-conflict constitution building through his work as president and co-founder of the Public International Law &amp; Policy Group. Williams is regarded as a social entrepreneur for his practical and innovative approach to providing "pro bono" assistance to clients. He has served as a delegation in the Dayton Agreement negotiations (Bosnia-Herzegovina), Rambouillet Agreement and Paris negotiations (Kosovo), Ohrid Agreement negotiations (Macedonia), and Podgorica/Belgrade negotiations for Serbia and Montenegro. He has also advised parties to the Key West negotiations for Nagorno-Karabakh, the Oslo and Geneva negotiations for the Sri Lankan Civil War, the Georgian–Abkhazian conflict negotiations, and the Somalia peace talks.