MEXICO CITY — Andres Manuel Lopez Obrador took the oath of office Saturday as Mexico’s first leftist president in over 70 years, marking a turning point in one of the world’s most radical experiments in opening markets and privatization.

In his first speech to Congress, Lopez Obrador pledged ‘‘a peaceful and orderly transition, but one that is deep and radical ... because we will end the corruption and impunity that prevent Mexico’s rebirth.’’

Mexico long had a closed, state-dominated economy, but since entering the General Agreement on Trade and Tariffs in 1986, it has signed more free trade agreements than almost any other country, and privatized almost every corner of the economy except oil and electricity.

Now, though, Lopez Obrador talks a talk not heard in Mexico since the 1960s: He wants to build more state-owned oil refineries and encourages Mexicans ‘‘not to buy abroad, but to produce in Mexico what we consume.’’

Even so, Lopez Obrador has tried to send conciliatory financial markets, which have been roiled in the weeks before he took office.

‘‘I promise, and I'm a man of my word, that the investments of foreign and international investors will be safe, and we will even create conditions that will allow them to get good returns,’’ he said, ‘‘because in Mexico there will be honesty, rule of law, clear rules, economic growth, and confidence.’’

But he also harkened back to his hero, ex-president Lazaro Cardenas, who nationalized the oil industry and redistributed land during his 1934-40 administration.

‘‘We are going to govern for everyone, but we are going to give preference to the most impoverished and vulnerable,’’ Lopez Obrador said. ‘‘For the good of all, the poor come first.'’’

Lopez Obrador also personally thanked US Vice President Mike Pence and President Donald Trump for the ‘‘respectful treatment’’ he has received from the US.

But Lopez Obrador was clear in blaming extreme market-oriented policies he calls neoliberalism for Mexico’s problems.

‘‘Mexico’s crisis originated not only with the failure of the neoliberal policies applied over the last 36 years,’’ he said in his inaugural speech, ‘‘but also in the prevalence of the filthiest corruption.’’

The rowdiest response from Congress came when Lopez Obrador pledged ‘‘not to persecute officials of past administrations,’’ saying ‘‘revenge is not my strong suit.’’

Legislators responded by counting loudly to 43 — the number of students kidnapped and disappeared in September 2014 — to remind Lopez Obrador of his promise to establish a truth commission to find out what happened to the students — a pledge he repeated Saturday.

Prosecutors have said they were kidnapped by corrupt police and turned over to a drug gang that killed them and burned their bodies.

Combined with a deep sense of nationalism and his own place in history, Lopez Obrador’s inauguration is the most home-grown, populist handover of power in decades.

As to underscore the transition, British Labour Party leaders Jeremy Corbyn showed up for inauguration after visiting Lopez Obrador a day earlier at his house in southern Mexico.

‘‘At a time when the fake populists of the far right are gaining ground internationally — including in Latin America,’’ according to a Labour Party statement issued in London, Lopez Obrador ‘‘has shown that a progressive agenda for change can win power and take on the status quo.’’

The country’s 65-year-old new leader is moving the presidential office fully back to the centuries-old National Palace that lines one side of the square, while refusing to live at the luxurious, heavily guard presidential residence 6 miles (9 kilometers) to the west. He will reside instead at his private home.

Closed to the public since the first parts were built in the 1930s, the compound will now be used for public events and it was thrown open to the public on Saturday.