Saied secured 2.7 million votes against one million received by his opponent, Nabil Karoui, in Sunday’s runoff vote, the commission said on Tuesday.
Karoui, a business tycoon who was in jail for most of the campaign, conceded defeat earlier on Monday.
The electoral commission said turnout stood at 55 percent, higher than during the first round on September 15, in Tunisia’s second free presidential election since the 2010-11 uprising that toppled long-standing ruler Zine El Abidine Ben Ali.
Saied, 61, is an independent candidate with no political experience. Backed by the conservative Ennahdha party, he has pledged to fight corruption and support decentralisation.
His austere demeanour earned him the nickname “Robocop” during campaigning, while his anti-establishment platform helped to woo younger voters disenchanted with politicians whom they accuse of failing to improve their lives since the Arab Spring uprising.
Some 90 percent of 18-to-25-year-olds voted for Saied, according to estimates by the Sigma polling institute, compared with 49.2 percent of voters over 60.
Following the release of exit polls on Sunday, Saied had described his projected victory as a “revolution within the constitutional legitimacy”.
“Thank you … to those who opened a new page in history,” he said. “For those who did not vote for me, thank you too, because they have chosen freely.”
Born in Ariana, a town close to the capital, Tunis, Saied spent most of his career teaching law at a university in Tunis, later serving as a member of the committee that supported parliament as it drafted the North African country’s post-revolution constitution, which was adopted in 2014.
He became known for delivering eloquent speeches to crowds in standard Arabic, rather than the Tunisian dialect during his campaign, as well as for his conservative views.
Saied is a supporter of the death penalty and opposes homosexuality, as well as equal inheritance for men and women – a proposal introduced by his predecessor, Beji Caid Essebsi, who died in July, five months before the end of his term.
Under Islamic law, a daughter inherits half the share a son does.
Saied now faces several challenges including social unrest, attacks by armed groups and an economic slowdown, three factors that have afflicted the country on its fledgeling democratic path.