MANILA — Ferdinand Marcos Jr., the son and namesake of the former dictator, was sworn in Thursday as the 17th president of the Philippines, praising his father’s legacy and pledging to confront an array of challenges as Rodrigo Duterte, the outgoing president, concluded a six-year term.
In a ceremony that capped a remarkable comeback for a family once forced into exile, Mr. Marcos, 64, presented himself as a leader who would help the Philippines improve its economy and secure a more prosperous future.
“You will not be disappointed, so do not be afraid,” Mr. Marcos said, speaking to thousands of supporters — including his 92-year-old mother, Imelda Marcos — at the National Museum of Fine Arts in Manila.
His victory has stoked concerns that another Marcos administration may return the country to its autocratic past. Not only did Mr. Marcos clinch the strongest majority vote in more than 30 years, but his allies also now control most of the House and the Senate.
His running mate, Sara Duterte, the daughter of Mr. Duterte, won the vice presidency with an even larger share of the vote. The president and vice president are elected separately in the Philippines. Ms. Duterte was inaugurated earlier this month.
In his inauguration speech, Mr. Marcos said his father’s administration built roads, produced rice and “never failed to defeat foreign attempts to break up our country.”
The scene surrounding Mr. Marcos’s inauguration on Thursday offered a vivid reminder of the challenges he faces in healing a country still scarred by the memories of martial law under his father.
Thousands of security forces stood guard as protesters gathered at a place called “Freedom Park,” about half a mile from the national museum. To many of the protesters, the Marcos name was a byword for excess, corruption and greed.
“The Marcos family should be made to pay for their sins and jailed, not celebrated,” said Marites Karganila, 53, a street vendor from a township south of Manila. Two of her cousins were jailed during the martial law years.
Opponents say Mr. Marcos has already demonstrated anti-democratic tendencies, pointing to how he has largely shunned the news media and broke with norms by refusing to participate in most of the presidential debates.
“I did not talk much in this campaign; I did not bother to think of rebutting my rivals,” Mr. Marcos said during his inauguration speech. Instead, he said he spent time searching “for promising approaches better than the usual solutions.”
Mr. Marcos, who goes by his childhood nickname, Bongbong, assumed the presidency as the country is trying to recover from the pandemic while managing rising inflation and mounting debt. He also inherited from Mr. Duterte a legacy of a drug war that has killed tens of thousands of people and prompted an investigation by the International Criminal Court.
The new president, who has previously indicated that he would not help the I.C.C. with its investigation into Mr. Duterte, signaled in his speech that he would reject all foreign interference in domestic politics. “We can trust no one else when it comes to what is best for us,” he said.
He pledged to improve the economy and to come up with an comprehensive infrastructure plan. Investors, however, have demonstrated little faith in his economic ability. Mr. Marcos placed near the bottom of a Bloomberg poll that asked investors and analysts who they thought would be the best candidate to lead the economy.
While several of his cabinet positions are yet to be filled, this month Mr. Marcos announced that he would take on the role of agriculture minister, an unusual move that would give him direct control over food prices, which have been rising. Defense, foreign affairs and health ministry positions remain vacant.
In his speech, Mr. Marcos also appealed to the more than one million Filipinos who left the country to find work abroad — as nannies, home health aides and seamen. These workers represent only about 2 percent of the population, but they have emerged as an important voting bloc.
“We are condemning the future of our race to menial occupations abroad,” Mr. Marcos said. He paid special tribute to nurses working overseas, recognizing that “they are out there because we cannot pay them for the same risk and workload that we have back here.”
Thursday’s inauguration came after a polarizing election. Leni Robredo, the country’s outgoing vice president, was Mr. Marcos’s main rival. Tens of thousands of her supporters campaigned door to door in a huge grass-roots movement determined to prevent a second Marcos presidency. But she placed a far second to Mr. Marcos.
Emerson Briones, an Orthodox archbishop, said he did not understand why people were protesting against the new president. He and dozens of Mr. Marcos’s followers celebrated the inauguration in front of the old Senate building. “I believe, as do all of us, that he will be the best president ever,” Archbishop Briones said. “We are in for an exciting ride.”
“It was a fair election,” he added. “The sins of his father, whatever they are, are not his.”
Jason Gutierrez reported from Manila and Sui-Lee Wee from Singapore. Camille Elemia contributed reporting from Manila.