Mark Ellis is the Executive Director of the International Bar Association (IBA). He served as Legal Advisor to the Kosovo Commission and advised the OSCE on the creation of Serbia’s War Crimes Tribunal. Dr Ellis worked alongside the ICTY, the Iraqi High Tribunal, the Cambodia Tribunal and presently with the ICC. In 2015, he was appointed to the UN Advisory Panel on Defence Counsel and in the same year launched eyeWitness to Atrocities, a mobile app for documenting war crimes. Since Russia’s invasion of Ukraine, Dr Ellis has led the IBA’s support efforts for Ukraine and, as a result, has been sanctioned by the Russian government. He was awarded Ukraine’s order of merit, one of Ukraine’s most distinguished state honours conferred by the President. His latest book, The UN Charter: Five Pillars for Humankind (Springer 2025), is co-authored with Ambassador David J Scheffer.

Where do you see the most exciting research/debates happening in your field?

One of the most important developments in international law is the increased use of universal jurisdiction. Universal jurisdiction is the idea that atrocity crimes, such as war crimes, genocide and crimes against humanity, are an affront to the world and every state can, and arguably must, prosecute these crimes. This is different from standard forms of jurisdiction, such as those based on the location of the acts or the nationality of one of the parties. There is an increased push to use universal jurisdiction, with over 50 cases open in 14 countries using absolute universal and over 100 more across 6 additional countries using either active or passive personality. In the last year, universal jurisdiction has been used by Finland to convict a Russian paramilitary leader for acts in Ukraine in 2014, and in Germany, Netherlands, and the United States against numerous former Syrian officials. Universal jurisdiction is not perfect, states are hesitant to risk overstepping their legal authority and there are difficulties gaining custody, but it provides a pathway towards justice where it otherwise has been denied. Even the threat of universal jurisdiction has an effect, limiting where those accused of serious crimes can freely travel without concern.

How has the way you understand the world changed over time, and what (or who) prompted the most significant shifts in your thinking?

The most dramatic change in my understanding of world affairs has been the rise of populism and nationalism. This phenomenon has emboldened the arbitrary exercise of state power. We are witnessing populist leaders targeting anything that criticises or constrains their authority. As a result, populists attack the media, the bureaucracy, universities, the judiciary, and civil society. Much of this is driven by loyalty to a populist leader who employs anti-establishment rhetoric to amplify perceived losses of cultural identity and economic security. Populists rail against multiculturalism, presenting themselves as the sole defenders of the “ordinary people.” Often, the populist leader is also a nationalist leader, characterised by an “us versus them” mentality and frequently accompanied by xenophobia, venomous intolerance, and the weaponisation of hatred toward others. The rise of both populism and nationalism over the past decade has been dramatic, and to me, deeply troubling.

You have described the UN Charter as “the world’s most important secular document.” At its core lies Article 2 and the prohibition of the use of force against the territorial integrity and political independence of states, a principle closely tied to the crime of aggression. At a time when this principle appears to be increasingly contested, how critical is the prosecution of aggression to the survival of the post-1945 international order?

I recently wrote in Just Security, that when the framers of the United Nations Charter enshrined Article 2(4) at its adoption in 1945 in the wake of the Second World........

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