Sidney is the Cofounder and Executive Director of Equiterre. Since then, as executive director, he has been involved in all of its activities, from development, to implementation, to funding. His passion for urban planning led him to chair the Montreal Regional Council on the Environment from 1996 to 2003. He also participated in efforts to increase funding for public transit in Quebec, as well as in Canada's ratification of the Kyoto Protocol. While in charge of energy initiatives at consumer protection group Option consommateurs from 1992 to 1998, Sidney helped set up a national energy-efficiency program for people with low incomes.
In 2007, he received a fellowship from Ashoka, an international organization that recognizes and supports social entrepreneurs. In 2009, he received the first Canadian Award for Environmental Innovation from the Royal Canadian Geographical Society. He is also an honorary fellow of the Royal Canadian Geographical Society. Sidney also spearheaded and chairs the Centre for Sustainable Development, which is one of the greenest buildings in Canada, as well as a hub for social and environmental groups.