Centre-left opposition candidate Alberto Fernández has been elected president of Argentina in a vote dominated by economic concerns, BBC reports.
Mr Fernández secured more than the 45% of the vote needed to win, beating conservative incumbent Mauricio Macri.
Raucous crowds gathered at Mr 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.
Mr Macri had trailed behind his challenger in pre-election polls and was trounced by the opposition in primary elections in August.
He conceded defeat on Sunday night. Congratulating his political rival, he said he had invited Mr Fernández to the presidential palace on Monday to discuss an orderly transition.
Mr 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, Mr Fernández had 47.79% of the vote, compared to Mr 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 10 December.