“Congratulations to Mamoudou Gassama for his act of bravery that saved the life of a child,” Ms Hidalgo tweeted.
“He explained to me that he had arrived from Mali a few months ago dreaming of building his life here.
“I replied that his heroic gesture was an example for all citizens and that the City of Paris will obviously be keen to support him in his efforts to settle in France.”
Hinting that he could expect a fast track to residency, government spokesman Benjamin Griveaux tweeted: “This huge act of bravery, faithful to the values of solidarity of our Republic, must open the doors to our national community.”
A petition has been launched online.
Rights group SOS Racisme said: “Mamoudou Gassama serves as a useful reminder to us that people without papers are human beings with…great bravery that many have shown in their perilous journey to Europe – bravery that they often continue to display here.”