Pietro Longo (born 29 October 1935) is an Italian politician.
Longo was born in Rome. His mother, Rosetta Longo, from Campobasso, was an old member of the Italian Socialist Party. Longo studied social sciences, and was one of the founder of the Censis (Italian Census Institute).
On 20 October 1978 he became secretary of the Italian Democratic Socialist Party (Partito Socialista Democratico Italiano, PSDI). He was confirmed as secretary in the party's 18th congress, held in Rome in February 1980, and in the 19th, held in Milan in March 1982. Longo was also minister for Economic Balance in Bettino Craxi's first cabinet.
In 1984 he had to resign first from his government position, and later (1985) as secretary, after the Loggia P2 scandal, whose members list included him since 1981. He was succeeded as PSDI secretary by Franco Nicolazzi. In the 1987 general elections he was not confirmed in the Parliament and lost judicial immunity. Longo thus underwent trial for the ICOMEC bribe scandal, being condemned in first (1989), second (1991) and third (1992) grade. The last condemnation caused him imprisonment in Rome's Rebibbia jail. In the meantime Longo had entered the Italian Socialist Party in 1989.