Andres Manuel Lopez Obrador could also end up proving a hard diplomatic partner for United States President Donald Trump with his vow to protect immigrants if his previous comments on the US President are anything to go by.
"Congratulations to Andres Manuel Lopez Obrador on becoming the next President of Mexico".
"There is much to be done that will benefit both the United States and Mexico!" tweeted the US Republican leader, whose anti-trade, anti-immigration policies have plunged bilateral ties between the neighbors to a historic low.
"While Obrador's victory may ease concerns of political instability, there still remains a thick smog of uncertainty over Mexico's economic outlook", said Lukman Otunuga of FXTM.
Lopez Obrador spoke to the crowd there around midnight, saying to loud applause: "Today one stage has ended and we are going to begin another one - we are going to transform Mexico!" Consequently, President Carlos Salinas de Gortari signed the North American Free Trade Agreement (NAFTA) in 1994, starting a new era of economic cooperation between Mexico and the US. "And I think that, at the very least, we need to, if we are going to-if this appointment is going to happen, at the very least we can do is delay the timeline in which women's healthcare is going to be taken away, delay the timeline in which our civil rights could potentially be further eroded".
Candidate Jose Antonio Meade of Pena Nieto's Institutional Revolutionary Party has been running third in most polls, behind front-runner Andres Manuel Lopez Obrador of the leftist Morena party and conservative Ricardo Anaya of a right-left coalition.
Supporters of Lopez-Obrador celebrated wildly in Mexico City.
Mexico's election tribunal says it will ratify the election results by no later than September 6.
The results make Obrador Mexico's first presidential candidate to receive more than 50 per cent of the vote since the PRI lost its dominant position in the last century.
Rating agency Moody's said on Monday that Lopez Obrador's election would result in short-term market volatility and represented risks for the oil sector.
Lopez Obrador arrived at a hotel in downtown Mexico City for the first of two victory speeches Sunday night in a bland white sedan befitting the "man of the people" image he has projected for over a decade.
He said the 2019 budget will include increasing pensions for the elderly and funds for his other campaign promises.
Mexican's President-elect has been a vocal critic of Donald Trump in the past.
U.S. Commerce Secretary Wilbur Ross told CNBC that Mexico "needs some sort of an arrangement" given its dependence on American consumers and businesses, having shipped $314 billion in goods to the United States previous year. "That is what brought us to this", she said.
The American Action Forum found in a report on December 11 that outright withdrawal from NAFTA would cost United States consumers and businesses up to $7 billion annually in increased prices, and could also jeopardize 14 million jobs and threaten almost $1 trillion in North American trade.
AMLO ran on a nationalist ticket and promised to be a lot less conciliatory than his predecessor towards the U.S., should he win the election.
Lopez Obrador will take office on December 1.