Born into a Roman Catholic family, he became a mechanic, just before the beginning of WW2, with the Société Nationale d'Étude et de Construction de Moteurs d'Aviation. After the collapse of France, he appears to have freely enrolled as a volunteer in Nazi Germany to work in the Messerschmitt aircraft manufacturing plant, as he left for Germany before the establishment of the STO system, by which French workers were compelled to work in German plants.
In 1946, he became secretary of the metalworkers' trade union in Issy-les-Moulineaux, and advanced in the Confédération générale du travail in his commune from 1951, becoming secretary of the Seine Metallurgical Workers' Union Federation from 1953 to 1956.
He entered the Party in 1947. In 1956, he was appointed a member of the extended Central Committee, and in 1959 a full member of it and of the Politburo. From 1961, he was the secretary in charge of the organization, then junior General Secretary in 1970. He co-signed the Common Programme with the Socialist Party (PS) and the Movement of Left Radicals (MRG) in June 1972. From 1973 to 1997, he was deputy of Val de Marne département, in Southern Paris suburb.
In reaction to the riots of May 1968, Marchais showed his contempt for Daniel Cohn-Bendit by calling him a German anarchist.
In December of 1972, he became General Secretary, following Waldeck Rochet's retirement. During his mandate, the PCF lost its place of "first left-wing party" to François Mitterrand's Socialist Party. At the beginning, he supported reforms in his party, which participated to Eurocommunism and renounced the proletariat's dictatorship (22nd congress, 1976). Then, faced with electoral growing of the PS at the expense of his party, he imposed a re-alignment on the Soviet Union at the end of the 1970s. The left-wing parties failed to update their Common Programme and lost the 1978 legislative election while they were favorites according to the polls. Outside and inside the party, he was accused to be responsible for this defeat. One year later, he supported the invasion of Afghanistan (1979), judged the Communist governments "fairly positive", and criticized the "right-wing drift" of the Socialist Party. Candidate at the 1981 presidential election, he was fourth in the first round, with 15% of votes, before endorsing Mitterrand, who won the second round.
In 1984, considering President Mitterrand had renounced to the left-wing Common Programme, the PCF ministers resigned from the cabinet. But the electoral decline ensued end he faced with some internal rebellions (Pierre Juquin, Claude Poperen, Charles Fiterman...) . He was reserved about perestroika. Contrary to the Italian Communists, he refused to change the name of the party after the collapse of the Soviet block.
In 1994, with the 28th Congress of the PCF, he ceded his place as General Secretary to Robert Hue, although he maintained his titular role as a member of the Politburo - significantly renamed National Office. The same year, he became President of the PCF Comité pour la défense des libertés et droits de l'homme en France et dans le monde ("Committee for the Defense of Human Liberties and Rights in France and Throughout the World"). He pronounced criticisms about the renovation of the party decided by his successor. He died in 1997.
Georges Marchais was a notable personality because of his mannerisms (Ct'un scandaaaale — "This is a scandal!") and brusque demeanor, often lambasted by comic Thierry Le Luron. He is particularly remembered for an outburst
During his TV performances, he had an aggressive and humorous tone with the journalists and his opponents. They stayed in the memory of the French audience. For instance, questioned by Elkabbach and Alain Duhamel about his economic propositions, he answered: "you are privileged, you hold many jobs and make good salaries (in TV, radio, papers...), probably you are concerned by my proposition for a wealth tax, I understand why you don't want the change!"