She spoke candidly about her drinking and drug use in a 5-minute video distributed by her father's staff, the New York Times reported.
The revelation came eight days before the inauguration of Bill de Blasio, whose campaign portrayed him with a happy and tight-knit family, the newspaper noted.
In the video, the young de Blasio talked about turning to drinking and drug use while battling depression as an adolescent. She said it got worse when she went to college in California last year.
"It didn't start out as like a huge thing for me, but then it became a really huge thing for me," she said in the video.
She has gone through outpatient group therapy, her father said.
The Times said the mayor-elect's staff described the video as an attempt to help others who might have similar issues this holiday season. The newspaper said for months de Blasio's aides had declined to respond to reporters' inquiries about his daughter's drug use, and added the nature and timing of the video's release suggested the family was intent on controlling how the story came out.
Standing with his family outside their home in Brooklyn, de Blasio said he was proud of his daughter for speaking out about her situation.
"If you look at this video, it speaks to a whole set of challenges that we face in our society," he said. "She speaks to it with incredible courage and clarity and, you know, with a voice that really suggests an incredible wisdom for someone who's only 19 years old."
Chiara de Blasio spoke briefly.
"I hope that everybody watches the video," she said. "I think it speaks for itself."
Her video drew the attention of White House Drug Policy Director Gil Kerlikowske, who said in a statement she "demonstrated tremendous bravery in speaking out about her recovery, and I applaud her and the entire de Blasio family for addressing this important public health issue."
"Chiara is giving a voice to the millions who suffer from substance use and mental health disorders, and we encourage others to join her," Kerlikowske said. "By talking about addiction in the light of day -- and by celebrating recovery out loud -- we can help correct the misinformation and stigma that too often become obstacles for the millions of Americans who deserve to live healthy, productive lives.
"Science clearly demonstrates that substance use disorders are a disease of the brain that can be prevented, treated and recovered from -- not a moral failing on the part of the individual."