He founded in 1959 the Combined Universities Campaign for Nuclear Disarmament and organized the first post-war student demonstration in Ottawa.
[5] In a recent interview, Roussopoulos stated that the mission of the publishing house was threefold: to disseminate ideas of participatory democracy and community organizing, to publish the best radical analysis of Canadian society, to revive libertarian socialist literature long suppressed on the left.
He helped found the Milton-Park Citizens' Committee and contributed to a decade-long effort to prevent the destruction of a heritage six-city-block neighbourhood.
[7] Roussopoulos was a president of the University Settlement of Montreal, which sought to democratize and localize the neighbourhood economy and successfully launched a credit union, a public library, and a rooftop garden.
[12] In 2012, he founded the Transnational Institute of Social Ecology, an Athens-based network of intellectuals and activists working in various cities in Europe.