In addition to his role as a professor and Legal Adviser, Chayes was also as one of the country’s leading authorities on international law. He served as lawyer, arbitrator, and consultant throughout his career. His cases ranged in topics from boundary disputes to class actions against foreign countries’ banking systems.
In 1980 Chayes represented the government of Nicaragua in a World Court lawsuit accusing the United States of illegally mining Nicaraguan ports and sending guerrillas to wreak destruction. Chayes received an overwhelming positive show of support from fellow Americans. When asked why he was representing Nicaragua, Chayes explained that there was “nothing wrong with holding the United States to its own best standards and best principles.” After years of arguments, and a withdrawal from the United States, the World Court found in Nicaragua’s favor in 1986. Unfortunately, the World Court had no enforcement power, and nothing ever came of the decision.
Chayes also served as head counsel for Namibia in its border dispute with Botswana over the status of Kasikili Island. Both countries claimed the under the Island under the terms of the Treaty of 1980 between Great Britain and Germany. Unfortunately, the World Court decided in favor of Botswana.
Before passing away in 2000, Chayes appeared in the news again. This time, he was representing two Kosovo Albanians living in the United States. They filed a suit against President Milosevic of Yugoslavia and a dozen others, accusing them of genocide and other war crimes.