Saied, a conservative academic with no previous political experience who won the overwhelming support of younger voters in an October 13 runoff, was sworn in before members of the constituent assembly and other top state bodies.
The poll followed the death in July of Beji Caid Essebsi, Tunisia’s first president freely elected by universal suffrage.
After sweeping 72.71 percent of the vote in this month’s runoff, Saied has won a clear mandate to fight corruption and promote social justice, even though his role focuses on security and diplomacy.
A constitutional law professor whose rigid and austere demeanour earned him the nickname “Robocop”, Saied has no real experience in foreign policy.
Tunis, which currently chairs the Arab League, could renew diplomatic ties with Syria, severed since 2012, and play a role in the return of the war-torn country to the bloc.
Saied has made strong statements against Israel, considering any ties with the Jewish state to be “high treason” — an Arab nationalist position that earned him praise among supporters.
While the security situation has significantly improved since a series of high-profile attacks on tourists in 2015, Tunisia has maintained a state of emergency for four years, with assaults against security forces persisting.
On June 27, a suicide attack killed two people in the heart of the capital Tunis, reviving the spectre of violence.
During the campaign debate, Saied said a key to fighting terrorism was education, arguing that improving primary education would “immunise” youth against extremism.
Another significant task he will face is reforming the police force, which was a cog in the dictatorship toppled by the Arab Spring revolt of 2011 and which continues to be accused of human rights abuses.