Mostafa Kamal Tolba led Egypt's delegation to the Stockholm Conference on the Human Environment in 1972, which launched a lifetime of commitment to environmental issues. After Stockholm he was nominated as Deputy Executive Director of the newly established UN Environment Programme (UNEP). Within two years, he became the Executive Director - a post he held until retiring at the end of 1992.
Under his leadership, UNEP became the core organization within the UN family to catalyze environmental action. His knowledge as a scientist, his skills as a negotiator, and his techniques of persuasion enabled him to bring people together to achieve what was thought to be unachievable and which contributed to the widely acclaimed Montreal Protocol - the historic 1987 agreement to protect the ozone layer, which is recognized as setting a precedent for international preventive rather than corrective environmental action.
In 1994 he established in Egypt the International Center for Environment and Development (ICED), a non-profit organization, which financed environmental projects in less developed countries.