A "lay" member (because he was elected by parliament in joint session) of the High Council of the Judiciary from 1976 to 1981, he was its vice-president during the last months of his mandate following the resignation of Ugo Zilletti.

Appointed constitutional judge by the President of the Italian Republic Sandro Pertini on January 25, 1982, he swears on February 3, 1982.

He served as Minister of Grace and Justice from 12 February 1993 to 9 May 1994, as an expression of the Catholic area but without belonging to any political party.

The first important measure of Giovanni Conso, taken on 21 February 1993, at the suggestion of the Minister of the Interior Nicola Mancino, was the revocation of a decree of his predecessor who had introduced the article 41-bis in Neapolitan prisons.

In an interview with the journalist Sandro Ruotolo in 2018, the then director of the Department of Prison Administration Nicolò Amato, speaking of this provision, states that he opened a door through which the State-Mafia Pact passed.