Video footage of Mamoudou Gassama scaling four floors of a the building with his bare hands has catapulted the young refugee to global fame and earned him the promise of citizenship from President Emmanuel Macron.
Wearing white tracksuit pants and a black cap, the hero of a rescue video viewed by millions of people appeared slightly overwhelmed by the media furore as he filed his application for legal residency in the Paris suburb of Bobigny.
Hailing the bravery of the youth who had been living in France illegally, the head of the local authority, Pierre-Andre Durand said: "How can anyone fail to be impressed by what he did, not admire it?
"He helped someone in danger, which is not such a common thing in our society."
Gassama became an overnight sensation after the video of him plucking a four-year-old boy to safety on Saturday went viral.
On Monday, he was honoured by President Emmanuel Macron with a medal for bravery, the promise of citizenship and the offer of a job with the fire service.
Gassama arrived in France via Italy and the perilous Mediterranean migrant route.
His official permit allowing him to work will arrive within a month, and his citizenship papers in about three months, officials said on Tuesday.
The athletic Malian also visited a fire station to sign up for a 10-month internship with the Paris fire and rescue services, expected to pay close to 600 euros ($920) a month.
'Could have been worse'
The family of the young boy he saved thanked him on Tuesday for his quick thinking.
The boy's paternal grandmother, who like his mother lives in Reunion, told RMC radio Tuesday that she was "very moved" by the images of the rescue and sent "huge thanks" to Gassama.
"He's really a hero," she said. "He did not stand by and watch, he saved my little sweetpea."
Malian migrant Mamoudou Gassama (C) flanked by his older brother (R) holds his temporary residence permit. Source: AFP
The boy's father, who had been living alone with him in Paris, had left him alone to go out to the shops and then remained on the street to play Pokemon Go, according to French investigators.
He was arrested on charges of neglecting his parental duties but released again on Monday.
The Paris prosecutor's office said he had admitted his guilt and expressed "profound regret".
The boy's mother learned the news of the rescue on Reunion Island - the French Indian Ocean territory where she and the father were born and where she still lives.
Reacting to Gassama's intervention on Antenne Reunion radio she said: "We can only thank him and thank heaven he was so reactive."
"Things could have turned out much worse so I am relieved," she said, adding that she was impatient to be reunited with her son and husband.
Gassama told Macron during a visit on Monday that he "did not think twice" before springing into action.
Lawmakers are debating a controversial bill that would speed up the deportation of economic migrants and failed asylum-seekers, thousands of whom live in squalid camps in the capital.
"There's a bit of hypocrisy or cynicism," added Claire Rodier of the GISTI association which supports immigrants. She saw a contrast between the treatment of Gassama and "the repressive policy of this government against migrants and those without documents."