Mohamed Ennaceur, who served Tunisia's acting president before the election, has hailed the country's smooth transition of power after Kais Saied was sworn in as new President.
61-year-old Saied took oath of office on Wednesday at the Assembly of People's Representatives' headquarters in the capital Tunis.
"This is a remarkable day because it represents an important transition in the lives of the Tunisians," Ennaceur said.
"What distinguishes Tunisia is the smooth transition of power that has not affected the continuation of the state," he added.
Saied won the second round of the presidential election on October 13 with 72.71 percent of the vote against his contender Nabil Karoui's 27.29 percent.
He becomes Tunisia's second democratically elected leader since the 2011 uprising.
"I swear by Almighty God to safeguard the independence of the homeland and the integrity of its territory, to respect the Constitution of the country and its legislation, to watch over its interests and to owe it allegiance," Saied said.
He pledged to fight terrorism in all its forms, saying "one bullet from a terrorist will be met with countless bullets."
Wednesday's inauguration was attended by senior officials of the country.