[3] Kallis earned a Bachelors in Chemistry with First Class Honours from Imperial College in London, where he continued to complete a master's degree in Environmental Engineering.

After a period at the European Parliament working at the Science and Technological Options Assessment Unit for the preparation of the EU Water Framework Directive, he completed a PhD at the Department of Environmental Studies at the University of the Aegean in 2003.

[12] In Barcelona he collaborates with economic historian Joan Martinez-Alier, with whom they set up the European Network for Political Ecology,[13] a training initiative for graduate researchers in the study of environmental conflicts.

Kallis has defined degrowth as a process of political and social transformation that reduces a society's energy and resource use while improving the quality of life.

[16] In March 2019 he wrote in favour of the Green New Deal resolutions presented in the 116th United States Congress, but argued that they should not be promoted in the name of growth.

Why Malthus was wrong and why environmentalists should care’,[23] Kallis makes a case in defense of limits, taking issue with the fantasy of modern societies with limitless expansion.