Jurors in Brooklyn federal court deliberated for a little more than a day before voting to convict the 54-year-old Kelly on all nine counts he faced, after a 5-1/2 week trial.
Kelly kept his head down as the verdict was read, with his face shielded by a white mask.
A woman watching from an overflow courtroom cried as the verdict was read, as did others who had waited to learn Kelly's fate in a park adjacent to the courthouse. One supporter played the singer's music there, including the song "Shut Up."
Deveraux Cannick, a lawyer for Kelly, told reporters that the defense was disappointed. "I'm sure we'll be appealing," he said.
Kelly faces a mandatory minimum of 10 years behind bars, and could face up to life in prison at his May 4, 2022, sentencing.
The singer, whose full name is Robert Sylvester Kelly, is one of the most prominent people tried on sex charges during the #MeToo movement, which amplified accusations that had dogged him since the early 2000s.
Like Kelly, many of his accusers were Black, differentiating the case from recent #MeToo convictions of comedian Bill Cosby and movie producer Harvey Weinstein. Cosby's conviction was overturned in June.
Kelly also had Black supporters.
One, Sylvia Tumusiime, said in an interview that the verdict left her "angry, upset and seeing that this is white American. White America," after she had attended the entire trial.
"I'm going to try to raise some money for him to try to get this appeal process started," said Tumusiime, from the state of Georgia. "I'm going hard and I'm not giving up. I'm not."
Kelly had been charged with one count of racketeering and eight counts of violating the Mann Act, which prohibits transporting people across state lines for prostitution.
The racketeering charge gave prosecutors leeway to offer evidence that might otherwise be too old to prosecute.
"We hope that today's verdict brings some measure of comfort and closure to the victims," Acting U.S. Attorney Jacquelyn Kasulis told reporters.
SHARING THEIR STORIES
Prosecutors said Kelly took advantage of his fame and charisma to recruit victims, including some plucked from crowds at his concerts, with the aid of people in his entourage.
Witnesses said some victims had hoped Kelly could jumpstart their careers, only to find he demanded their strict obedience and would punish them if they failed.
Trial testimony from the 45 government witnesses portrayed, often in graphic detail, an unseemly side to Kelly's 30-year music career, whose highlights include the 1996 Grammy-winning smash "I Believe I Can Fly."
Kelly has repeatedly denied sexual abuse accusations.
His alleged victims included the late singer Aaliyah, who Kelly briefly and illegally married in 1994 when she was 15. Aaliyah died in a 2001 plane crash.
Many accusations against Kelly were included in the January 2019 Lifetime documentary "Surviving R. Kelly."
"We commend the survivors for their bravery in speaking out and sharing their stories," Lifetime and the documentary's producers said in a joint statement. "They have opened up important conversations on sexual abuse that needed to happen."
Several witnesses testified that Kelly instilled fear if his victims did not fulfill his every need, sexual and otherwise.
Jurors heard how Kelly would compel victims to follow "Rob's rules," including that they call him "Daddy" and get permission to eat or go to the bathroom.
Witnesses said Kelly pressed accusers to write "apology letters" to potentially absolve him of wrongdoing, and concealed before intercourse that he had contracted herpes.
'NO MARTIN LUTHER KING JR.'
One witness, who identified herself as Sonja, testified she had hoped to interview Kelly for a radio station where she was interning, when he locked her up for at least two days without food or water and then assaulted her.
"I've been hiding from Robert Kelly in fear," Sonja said in a statement read by her lawyer Gloria Allred. "I'm ready to start living my life free from fear and to start the healing process."
Allred alluded after the verdict to Cannick's closing argument where he invoked the civil rights leader Martin Luther King Jr. in urging jurors to show courage and acquit Kelly.
"Despite the fact that he thought he could control all of his victims, he was wrong," Allred told reporters, referring to Kelly. "Based on the evidence, the jury must have concluded that R. Kelly is no Martin Luther King Jr."
Kelly did not testify in his defense.
His lawyers had sought to portray Kelly's accusers as former fans who felt jilted when they fell from his favor, and that their sex with Kelly was consensual.
They also tried to show how some accusers stayed with Kelly long after the alleged abuses began, and questioned why they failed to go to the police or waited years to come forward.
On top of the conviction, Kelly still faces federal charges in Chicago on child pornography and obstruction, and state charges in Illinois and Minnesota.