In 1953 he was one of the founders of the Christian Democracy (Democrazia Cristiana). He later was appointed as party's provincial secretary of Milan and vice-secretary national. In 1968 he became senator for the college of Vimercate. Between 1970 and 1975 and from 1980 until his death he was also mayor of Inveruno.
In 1974 Aldo Moro called him as minister of Agriculture in his cabinet, a position that Marcora held uninterruptedly until 1980, before moving to the Ministry of Industry in 1981–82.