Mariotto Segni, more often known as Mario, (born May 16, 1939 in Sassari) is an Italian politician, son of Antonio Segni, one time President of the Republic of Italy.
A long-time member of Christian Democracy, he was first elected regional councillor in 1967 and then he was deputy from 1983 to 1996.
In 1992 he founded the Populars for the Reform, whose principal aim was electoral reform from proportional representation to a first-past-the-post system, and the Patto Segni in 1993.
He was candidate for Prime Minister for the centrist alliance Pact for Italy (composed of Italian People's Party and Patto Segni) in 1994 and MEP from 1994 to 1995.
In 1999 he was elected MEP on a National Alliance-Patto Segni list.
In 2003 he refounded the Patto Segni, naming it Pact of Liberal Democrats.
In 2007, Mario Segni, along with politicians such as Gianni Alemanno, Angelino Alfano, Mercedes Bresso, Riccardo Illy, Renato Brunetta, Antonio Martino, Giovanna Melandri, Arturo Parisi, Daniele Capezzone, Stefania Prestigiacomo, Gaetano Quagliariello, Giorgio Tonini, a referendum aimed at changing the electoral system. The referendum, that took place on June 21-22, 2009, did not reach the required quorum.