Institutional reforms being debated in Parliament propose giving voters a greater say in electing the prime minister, who under the current constitutional rules, is appointed by the president. “Renzi envisions a system where the prime minister has the direct support of voters, and the reins of power, and the president as being more representative of Italians,” Mr. Damilano said. Mr. Mattarella, he added, is seen as well suited for that role.

But reforms under discussion to change the electoral law and the makeup of Parliament are leaning toward reinforcing the executive branch, which could create potential conflicts for a president, who under the Constitution has the right to dissolve Parliament and name a prime minister.

With the new electoral law, “people expect to choose the head of the government,” said Roberto D’Alimonte, a political analyst at the Luiss Guido Carli University in Rome. “So what happens if he is removed because of an internal party coup, or the majority party splits, and a new government is formed with different political parties? What will be the role of the president? If everything goes smoothly, there’s no problem, but if it doesn’t, then the role of the president will be tricky.”

Mr. Mattarella was born in Palermo, Sicily, in 1941 and went on to study law. His older brother, Piersanti, who was the governor of the Sicily region, was killed by the Mafia in 1980.

Mr. Mattarella was first elected to office in 1983 as a member of the Christian Democratic Party, which dominated postwar Italy until it imploded after a series of bribery scandals in the early 1990s. He went on to hold a number of high-level government posts under the Christian Democrats and in later center-left governments. He served in Parliament until 2008. In 2011, he was elected by Parliament to Italy’s Constitutional Court.

Mr. Mattarella’s victory came without much of the high drama that normally exists during Italy’s presidential elections, including the settling of scores and horse-trading. Two years ago, this Parliament was unable to break a deadlock as it tried to elect a successor to President Giorgio Napolitano at the end of his seven-year term. Mr. Napolitano, now 89, agreed to stay on temporarily. He resigned this month, citing his advanced age.