Gendron was re-elected in the 1965, 1972, 1974, 1979 and 1980 elections.
He left federal politics after serving six terms from the 27th to the 32nd Canadian Parliaments.
Between 1956 and 1968 he was mayor of Rivière-du-Loup, Quebec, also serving as president of the Union of Quebec Municipalities in 1964–1965.
He also served as executive vice-president for the Chamber of Commerce of Quebec at one time.