The estimate by two polling companies saw Hidalgo, with between 49.3 and 50.2 percent of the vote, ahead of right-wing candidate Rachida Dati, with President Emmanuel Macron's candidate a distant third.
Speaking on Sunday night Hidalgo thanked all those who had voted for her
“You chose hope, you chose unity, you chose a Paris that breathes, a Paris that will be more pleasant to live in, a more united city, which leaves no one on the side of the road,” she said.
“I hope that all the forces working in service of our fellow citizens are involved in the transformation of our city, which is all the more urgent because of the crisis we are going through.
“During this mandate, we will experiment with other ways of bringing Parisian democracy to life, in order to give a taste of our commitment to all those who love their city,” she added.
“With you we will build the Paris of tomorrow,” Hidalgo said.
“A Paris that gives resources to its public services so that they can carry out their missions, in particular for the health of Parisians.
“A Paris that allows everyone to change their way of life, to move better, to eat better, with respect for our environment as a common value.
“A united Paris that helps those who need it most. A Paris of difference that fights all forms of discrimination.
A Paris that gives its youth a real chance and that gives them the keys to act.”
As mayor, Hidalgo has pushed to reduce car use in the capital and boost biking.
She has reduced lanes and speed limits, closing off dozens of streets to cars completely.
In her latest campaign, she has proposed transforming 60,000 roadside parking spaces into cycling lanes.
But the move has proved controversial among many drivers who complain the city is a perpetual building site.
Hidalgo has also pledged to improve sanitation in the city plagued by rats, bed bugs and dirty streets.
Her unsuccessful challenger Agnes Buzyn of President Emmanuel Macron's Republic on the Move (LREM) party described Paris during her campaign as “brutal for its inhabitants, a city whose condition has deteriorated”.
Hidalgo has said sanitation will require a yearly one-billion euro ($1.12 billion) city budget.
Another challenge is the sky-high property costs driving some 12,000 people out of Europe's densest city each year.
Hidalgo has promised major investment in housing, transport and green spaces, seeking to reverse the middle- and working-class exodus to the suburbs.
Analysts expect the election to confirm that Macron's centrist Republic on the Move (LREM) party — founded by the president ahead of his 2017 election win — has failed to gain a strong foothold at local level.
The party made lacklustre showings in March — notably in Paris where Macron's candidate, former health minister Agnes Buzyn, came third.
“The problem is that the LREM is a new party that has no local roots and is struggling to impose itself as a (political) force,” analyst Jean Garrigues of the University of Orleans told AFP.
Amid persistent fears of coronavirus contagion, just over a third of voters had turned out by 5:00 pm, three hours before polling stations close, the interior ministry said.
The turnout rate of 34.67 percent was lower even than nine hours into the first round of voting on March 15 that was marked by a record 55-percent abstention rate.