The French government decided to award citizenship to the Malian-born 24-year-old supermarket employee after he risked his own life to hide customers from hostage-taker Amedy Coulibaly earlier this month.
Four people lost their lives in the hostage-taking and shooting at the kosher grocery store. But the 15 people whom Bathily led downstairs to hide
in a walk-in freezer stayed safe.
Bathily, who describes himself as a "practicing Muslim," told CNN affiliate BFMTV he switched off the freezer, turned off the lights and told everyone to stay calm. He went upstairs, following orders from the hostage-taker, but managed to run outside and tell police about the situation in the store.
In his opening speech at the ceremony Tuesday evening, Cazeneuve praised Bathily's gesture "of courage and humanity" which had become "the symbol of an Islam of peace and tolerance."
Bathily, who arrived in France when he was 16, had dreamed of gaining French citizenship since his childhood.
"Today, this dream is becoming true, a bit faster than expected," Cazeneuve said.
Valls also paid tribute to the courage of the young man. "With you and with all the people in this room," the Prime Minister said, "we just saw one of the most beautiful images of our country."
Valls also recalled the strong ties between France and Mali, a "country which saw Timbuktu being wrecked by terrorists," and which received French support in its fight against jihadism. The French military has been involved in fighting Islamist extremists in Mali and the wider Sahel region since early 2013.
Both Valls and Cazeneuve emphasized the importance of keeping French citizenship open in order to remain faithful to the Republican ideal.
"Welcoming new French citizens is an opportunity for the country as well as for those who become French," Valls said.
Bathily then took the floor. "I thank you with all my heart for awarding me French citizenship. I am proud and moved," the young man said.
"People think I am a hero, but I am not. I am just Lassana."
At the end of the ceremony, Bathily received his passport together with a letter from President Francois Hollande and the "citizenship kit" distributed to all new French citizens.
Coulibaly, the terrorist killed in the police operation that ended the supermarket attack, also had roots in Mali. But, unlike Bathily, he was born in France and had French citizenship.