In 1991 he was appointed adviser to the criminal affairs department of the Ministry of Justice, whose minister was Claudio Martelli, whom he named Giovanni Falcone, and member of the Central Commission for the repentant.

He was then replaced in his role, until he was appointed deputy prosecutor at the National Anti-Mafia Directorate (led by Pier Luigi Vigna), applied in the Procure of Palermo and Florence, where he supervised and coordinated the investigations on the massacres of 1992 and 1993.

The gangs in question are The Rose of Tropea and that of Mancuso Limbadi that ricavavano huge profits from the control of contracts for the construction and supply of holiday villages in the area of Catanzaro.

From September 2012 to Rai History in 12 episodes, Pietro Grasso leads "Lessons Mafia", a project of legal education, dedicated to the younger generations to explain all the secrets of Cosa Nostra.

The program is inspired by the lessons mafia devised in 1992 by the Director of TG2 Alberto La Volpe with Giovanni Falcone, one of the last initiatives of the magistrate from Palermo crushed by the attack of Capaci.

[3] In March, following the general election, along with many other colleagues in the Italian Parliament, Grasso joined the project "starts again in the future" by signing the petition that aims to review the anti-corruption law by changing the norm on the exchange-electoral political mafia within the first hundred days of parliamentary activity.

[11][12][13] On 3 December 2017, Grasso was appointed leader of Free and Equal (LeU), a left-wing political alliance of parties, formed by the Democratic and Progressive Movement, Italian Left and Possible.