On his return from graduate studies in Sweden, MacNeill began his public service career in Saskatchewan in 1952 as a research economist in T. C. Douglas' cabinet's Economic Advisory and Planning Board.
In 1959, he became Executive Director of the South Saskatchewan River Development Commission with responsibility for coordinating the power, irrigation, and other aspects of that project.
Moving to the international arena in 1977, Jim MacNeill served for seven years in Paris as Director of Environment for the Organization for Economic Cooperation and Development (OECD).
[3][4] In 1994, as an advisor to Netherlands Prime Minister Ruud Lubbers, he negotiated an agreement between Mikhail Gorbachev as the Chairman of Green Cross International and Maurice Strong as the Chairman of the Earth Council to undertake the development of an Earth Charter, a code of ethical principles which has now been endorsed by over 8,000 organizations representing more than 100 million people worldwide.
In 1990, he was one of three founding members of the International Institute for Sustainable Development, an initiative of Prime Minister Brian Mulroney of Canada and Premier Gary Filmon of Manitoba, and served as Chairman between 1994 and 1999.
[7] Maurice Strong was a close adviser to former UN Secretary General Koffi Annan and became embroiled in what is now known as the Oil for Food Program Scandal and reportedly received millions of dollars from North Korean and Iraqi lobbyists.
Strong is credited in assisting with the creation and submission of the 1987 Brundtland Report (called "Our Common Future") that would be presented to the UN General Assembly and become the basis for the 1992 Earth Summit.