[1] A member of the Christian Democracy party, Segni held numerous prominent offices in Italy's post-war period, serving as the country's Minister of Foreign Affairs, Interior, Defence, Agriculture, and Public Education.

He grew up in a well-off family, involved in Sardinian politics; his father served as municipal and provincial councilor for Sassari, as well as deputy mayor during the early 1910s.

[4] He completed his studies in Rome with Giuseppe Chiovenda, of which he became the favorite student; in the law firm of the jurist, he met Piero Calamandrei, with whom he built a close friendship that would last a lifetime.

In 1921, he married Laura Carta Caprino (18 April 1896 – 21 July 1977)[6] daughter of a rich landowner,[7] with whom he had four children,[8] including Mario, who would become a prominent politician during the early 1990s.

For the next 17 years, Segni left political life, continuing to teach civil procedure and agrarian law at the universities of Pavia, Perugia, Cagliari, and Sassari, where he later served as rector from 1946 to 1951.

[19] Segni's reform proposed, through forced expropriation, the distribution of land to agricultural labourers, thus making them small entrepreneurs and no longer subject to the large landowner.

[20] If in some ways the reform had this beneficial result, for others it significantly reduced the size of farms, effectively removing any possibility of transforming them into advanced businesses.

[23] Modern historians assert that landowners were instead favoured by Segni, and his decrees allowed them to reclaim land that had been granted to the peasantry by the preceding administration.

[25] As minister, Segni was particularly involved in the fight against illiteracy, in the improvement of teaching activities, and in the construction of new schools around the country; however, he did not continue the important reforms started by his predecessor.

The change was strongly opposed by both the opposition parties and DC's smaller coalition partners that had no realistic chance of success under this system.

[29] Frustration with the failure to win a supermajority caused significant tensions in the leading coalition, and De Gasperi was forced to resign by the Italian Parliament on 2 August.

[40] In March 1957, Segni signed the Treaty of Rome, which brought about the creation of the European Economic Community (EEC), between Belgium, France, Italy, Luxembourg, the Netherlands, and West Germany.

[43] As premier, he also had to face the complicated Suez crisis of 1956, in which he staunchly defended Italy's economic interests in the area, always bearing in mind the need to safeguard Atlantic and European solidarity.

[49] As minister, Segni worked to represent the interests of the Italian Armed Forces, increasing wages and social securities for retired veterans, as well as strengthening military equipment and weapons.

[50] He also accepted NATO missile bases for atomic weapons, convinced that they were a necessary tool to ensure the defence of Italy more than a danger that exposed the country to possible reprisals.

[53] Segni formed a one-party government, which was composed only by DC members, and was externally supported by minor centre-right and right-wing parties, as well as the neo-fascist Italian Social Movement (MSI).

The most comforting signals came from the economy, as industry and commerce expanded, unemployment declined, and Italy's GDP grew by over 6%, a rhythm that placed it among the most dynamic countries in the world.

After few months of Fernando Tambroni's government, Fanfani returned to the premiership on 26 July, this time with an openly centre-left program supported by the PSI abstention, and Segni was appointed Minister of Foreign Affairs.

[58] In May 1962, when Gronchi's term as president of Italy expired, Segni was proposed as the DC's candidate by new party's leader Aldo Moro for the 1962 presidential election held on 2–6 May.

With Segni's choice, Moro wanted to reassure the conservative representatives of his own party, worried about a possible extreme shift on leftist stances, after the beginning of the organic centre-left period in February 1962.

[59] On the first two rounds, the Italian Communist Party (PCI) decided to vote for Umberto Terracini, while the PSI supported Sandro Pertini.

[64] Many influent entities, notably including the Bank of Italy, the Armed Forces, Vatican hierarchies, as well as economic and financial world, were concerned about the entry of the PSI into the government, and considered Segni a reference of stability and their most prominent political landmark.

[72] The DC accused the PCI of political profiteering from the tragedy and then-prime minister Giovanni Leone promised to bring justice to the people killed in the disaster.

A few months after the end of his premiership, he became the head of SADE's team of lawyers, who significantly reduced the amount of compensation for the survivors and ruled out payment for at least 600 victims.

[74] On 16 July, Segni sent the Carabinieri General Giovanni De Lorenzo to a meeting of representatives of the DC, to deliver a message in case the negotiations around the formation of a new centre-left government would fail.

[82] During all his political career, Segni acted as a moderate conservative, staunchly opposing the "opening to the left" proposed by Fanfani and Moro, but he also tried not to bring his own party too far to the right.

On 25 March 1964, De Lorenzo met with Carabinieri's commanders of the divisions of Milan, Rome, and Naples, proposing a response to a hypothetical national crisis, known as Piano Solo.

[86] The plan consisted of a set of measures to occupy certain institutions, such as Quirinal Palace in Rome, and essential media infrastructures, like television and radio, as well as the neutralisation of communist and socialist parties, with the deportation of hundreds of left-wing politicians to a secret military base in Sardinia.