Anne Hidalgo said that the exact location of the "humanitarian camp" would be revealed in the next few days after an inspection of possible sites.
Hundreds of migrants have been camping rough in the city.
Meanwhile, the death toll from migrant shipwrecks in the Mediterranean last week was revised upwards to 1,000.
International Organization for Migration (IOM) spokesman Flavio Di Giacomo gave the new figure which comes after an estimate on Sunday of 700 deaths by the UN refugee agency.
The new camp in Paris is expected to provide both day facilities and overnight accommodation.
"We are going to work extra hard on this," the Socialist mayor told reporters.
The current situation, she said, was no longer "tenable", citing a makeshift camp that had sprung up in the north of Paris in the past few days, which is now home to 800 people.
The new camp, she added, would be modelled on one created near the northern port of Calais to take in people from the unofficial "Jungle" encampment.
Calais and Dunkirk, which also has an official camp, are seen by undocumented migrants as gateways to the UK.
Few of those passing through the French capital en route to other countries say they plan to settle there, the BBC's Lucy Williamson reports from Paris.
Tweeting on Tuesday, the IOM spokesman noted that 2,400 migrants had lost their lives in sea crossings since January.
The number of arrivals, he said, were the same number as in January-May of last year but the death toll had risen by 34%.
Spring weather has led to a surge of people attempting the perilous crossing from Africa to Europe.
It is now a key route for undocumented migration since a deal curbed numbers making the much shorter crossing from Turkey to Greece.
A note on terminology: The BBC uses the term migrant to refer to all people on the move who have yet to complete the legal process of claiming asylum. This group includes people fleeing war-torn countries such as Syria, who are likely to be granted refugee status, as well as people who are seeking jobs and better lives, who governments are likely to rule are economic migrants.
A camp for migrants is to be set up in the north of Paris within the next six weeks, the mayor of the French capital has announced.