Alberto Fernández has been elected president of Argentina in a vote dominated by economic concerns.
The center-left opposition candidate secured more than the 45% of the vote needed to win, beating conservative incumbent Mauricio Macri.
Raucous crowds gathered at Alberto Fernández’s election headquarters to celebrate the result.
The vote was held amid an economic crisis that has left a third of Argentina’s population in poverty.
Mauricio Macri had trailed behind his challenger in pre-election polls and was trounced by the opposition in primary elections in August.
The incumbent president conceded defeat on October 27. Congratulating his political rival, Mauricio Macri said he had invited Alberto Fernández to the presidential palace on October 28 to discuss an orderly transition.
Alberto Fernández later told supporters he would collaborate with the outgoing president “in every way we can”, according to Reuters.
With more than 90% of ballots counted, Alberto Fernández had 47.79% of the vote, compared to Mauricio Macri’s 40.71%.
To win in the first round, a candidate needs at least 45% of the vote, or 40% and a 10-point lead over the second-place contestant.
Alberto Fernández will assume the presidency on December 10.
The vote was dominated by concerns over the economy. With nearly one in three people now living in poverty, voters backed the candidate they thought was best-placed to lead Argentina out of the crisis.
Mauricio Macri promised to achieve “zero poverty”, but things actually worsened during his four-year rule. His supporters say he inherited a broken economy when he came to power and needed more time to sort it out.
Alberto Fernández has vowed to play things safe financially.
Career politician Alberto Fernández has caused quite a stir since he first appeared in the limelight of Argentine politics some six months ago.
The former campaign strategist began his bid for the presidency in May – something of a surprise as ex-president Cristina Fernández de Kirchner had been widely tipped to be the center-left opposition coalition’s candidate for the top office.
However, Alberto Fernández really came into his own in August when he defeated Mauricio Macri by nearly 15 percentage points in primary elections, a compulsory vote for all electors which is seen is a dry-run for the presidency.
Mauricio Macri has been sworn in as Argentina’s president in a Buenos Aires ceremony.
The newly-elected president vowed to unite the nation and revive the economy.
The center-right Mauricio Macri took the oath of office in Congress but his inauguration was boycotted by his predecessor, Cristina Fernandez de Kirchner, in a row over the venue.
In his inaugural speech, Mauricio Macri vowed to tackle corruption, poverty and drug trafficking.
He also pledged “team work” and an end to confrontation in politics.
Mauricio Macri, 56, told Congress: “As president I want to be a citizen who can communicate with all Argentines.
“Politics for me is not a competition to see who’s got the bigger ego. It’s working together for the good of the people.”
“Today a dream is being achieved,” he said.
On December 9, outgoing President Cristina Fernandez de Kirchner had bid farewell to supporters in an emotional speech, urging people to take to the streets if they felt betrayed by the new centre-right government.
This is the first time since the end of the military dictatorship in 1983 that a president has not attended the inauguration of a successor.
Mauricio Macri triumphed in last month’s election run-off, beating Cristina Fernandez’s chosen successor, Daniel Scioli.
The newly-elected president has promised to move from a largely state-controlled economy under the leftist Cristina Fernandez de Kirchner to one that is more free market-orientated, easing trade and currency controls.
Mauricio Macri has also promised to improve relations with the US.
In his speech in Congress he said: “We’ve got to take confrontation out of the centre of politics. With fighting no-one wins, with dialogue, everyone wins.
“A new time is coming, a time of dialogue, a time of teamwork.”
Mauricio Macri said those who had voted for him wanted three goals – zero poverty, an end to drug trafficking and the unity of all Argentines.
To applause, he said he wanted a judiciary cleaned of its political affiliations.
Marta Gabriela Michetti was sworn in as vice-president.
Mauricio Macri then travelled to the presidential palace to receive the sash and baton of office.
Cristina Fernandez de Kirchner had insisted that the handover of the symbols of office should also take place in Congress, where her party holds a majority of seats.
She argued this was a tradition established by her and her late husband and predecessor in office, Nestor Kirchner.
Mauricio Macri argued that according to presidential protocol, the handover should be held in the palace, as it was before 2003.
Local media reported that Mauricio Macri’s decision was probably driven not just by tradition but also by a concern that followers of Cristina Fernandez de Kirchner could disrupt the ceremony in Congress.
After Cristina Fernandez de Kirchner declined to attend the ceremonies, Mauricio Macri’s party sought a court injunction affirming that her term ended at midnight on December 9.
Argentina is voting to choose the country’s next president in a general election that ends 12 years of rule under the Kirchners.
President Cristina Fernandez de Kirchner has served two consecutive terms and, under Argentina’s constitution, cannot run again.
Cristina Fernandez’s hand-picked successor, left-winger Daniel Scioli, is leading polls.
However, Daniel Scioli he is expected to face stiff competition from Mauricio Macri, the centre-right mayor of Buenos Aires.
Another candidate, Sergio Massa, a former Kirchner ally, is polling behind Mauricio Macri, while there are three other names on the ballot paper.
Today is the first round of voting – if no candidate gets more than 45% of the vote, or gets a minimum of 40% as well as a 10-point lead, there will be a run-off on November 22.
Whoever wins the presidency faces significant economic challenges.
While Argentina gained strength after a financial crisis in 2002, its economy, the third largest in Latin America, has slowed down in recent years, with GDP growing by only 0.5% in 2014.
The government is also locked in a battle against American hedge funds who disagree with how is wants to restructure $100 billion of debt on which it defaulted in 2001.
While the companies successfully sued Argentina for repayment, Cristina Fernandez de Kirchner refused to pay.
She succeeded her husband Nestor Kirchner as president. He died in 2010, three years after handing over the presidency to his wife.
Daniel Scioli, the governor of Buenos Aires province, is a former world powerboating champion who lost his right arm in a boat race in 1989.
Last week, he pledged tax cuts for middle-class workers earning under a certain income, a move expected to affect half a million people.
Daniel Scioli has also vowed to bring down Argentina’s inflation to single digits in less than four years and promises to introduce policy changes to invigorate the economy.
Like Daniel Scioli, Mauricio Macri is married to a former model. He is a former president of Boca Juniors, Argentina’s most successful soccer club.
While Cristina Fernandez de Kirchner has sought to press Argentina’s claims for the disputed UK territory of the Falkland Islands, Daniel Scioli says he would not appoint a Falklands minister, and would seek closer ties with London.