Carbonneau is a left-wing political activist who advocated violence. He joined the Front de Libération du Québec terrorist organization that advocated the use of violence to achieve their goals, calling for a Marxist/anarchist insurrection, the overthrow of the Quebec Government, the separation of Quebec from Canada and the establishment of a workers' society. Members of the Front de Libération du Québec received guerrilla training in selective assassination from Palestinian commandos. From 1963 to 1970, the FLQ committed over 200 violent crimes, including robberies of dynamite, bombings, bank hold-ups, and at least three violent deaths by FLQ bombs and two murders by gunfire.
In 1966 a secret eight-page document entitled "Revolutionary Strategy and the Role of the Avant-Garde" was prepared by the FLQ outlining its long-term strategy of successive waves of robberies, violence, bombings and kidnappings, culminating in insurrection and revolution. A member of the FLQ’s “Liberation Cell,” that included Louise Lanctôt, Jacques Cossette-Trudel, Jacques Lanctôt, Yves Langlois and Nigel Hamer, on October 5, 1970 they put their kidnapping plans into action with the armed abduction of James Cross, the British Trade Commissioner to Canada.
Marc Carbonneau and other members of the Liberation cell, will hold James Cross hostage, taking his photo and sending it to police with a list of demands that included money and the release of other convicted terrorists. They advise authorities that Cross will be executed and further threats to Cross’ life were delivered to several radio stations along with the terrorists demands. This action was followed by a second kidnapping of Quebec Cabinet Minister and Vice-Premier Pierre Laporte by his “Chenier Cell” counterparts. Laporte will be abused by his captors and then executed.
Early in December of 1970, police discovered the location of Marc Carbonneau and his fellow terrorists holding James Cross. His release was negotiated and on December 3, 1970, Carbonneau plus the four other terrorists, were granted their request for safe passage to Cuba by the Government of Canada after approval by Fidel Castro. Although Carbonneau had asked to go to communist Cuba and was exiled from Canada for life, he secretly left Cuba to live in Paris, France. After a few years there, he wanted to return to Canada and began secret negotiations through the reigning government Parti Québécois to achieve that goal. Eventually, the Federal Government consented and Carbonneau returned to Canada from Paris on May 25, 1981. He is charged with conspiracy, forcible detention and extortion in connection to the kidnapping of James Cross. He plead not guilty and was released on bail. On October 22, he went back to court and changed his plea to guilty in the kidnapping of James Cross.
On March 23, 1982, Marc Carbonneau was sentenced to 20 months in jail for kidnapping, forcible confinement, conspiracy and extortion.