United Medical Center spokeswoman Natalie Williams confirmed the former mayor's death, but declined to give further details.
The Washington Post, citing hospital officials, said the mayor was in cardiac arrest when he arrived at the hospital and could not be revived.
Local media said he had only just been released from another area hospital earlier in the evening after being admitted Thursday for observation, after what the local NBC affiliate reported was a urinary tract infection.
Barry, the Mississippi-born son of a sharecropper and a leader in the civil rights movement, dominated local politics in the US capital for decades, despite repeated scandals and multiple arrests.
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The most notorious incident came during his third term as mayor when he was arrested in January 1990 for crack cocaine use and possession in an FBI sting operation caught on video.
The "mayor for life" was sentenced to six months in prison, but swept back into the city's top post in 1994.
More recently, in 2009, Barry, who was serving again as a city councilman, was arrested for allegedly stalking a woman.
In his early terms Barry gained recognition as a charismatic leader who used the city administration to further his ambitious social programs including jobs for the poor.
In his DC Council biography, Barry wrote that he lived by the motto "always fighting for the people."
But by his later terms Barry's fortunes and those of the city had begun to sag. The municipal deficit ballooned, crime rose, and a close mayoral confidant was convicted for misuse of public funds.