The judge told the court he was remanding Conrad Murray in custody without bail because he was a convicted felon and a flight risk
A panel of seven men and five women took two days of deliberation to reach a verdict.
Michael Jackson died on 25 June 2009 from an overdose of the powerful anaesthetic propofol.
Murray, 58, could now receive a maximum prison term of four years and lose his licence to practise medicine.
There was a shriek in the courtroom as the verdict was read.
Outside the courthouse, the BBC's Peter Bowes said that at the moment the verdict was read, the crowd along the street erupted with cheers and chanting.
Jackson's family sat in the courtroom, weeping quietly.
LaToya Jackson told the Associated Press news agency the family was overjoyed at the verdict.
"Michael was looking over us," she said.
During the trial, Dr Murray's lawyers argued that Jackson self-administered a lethal dose of the drug while he was out of the room.
When the verdict was announced there was a stifled scream in the courtroom from the Jackson family entourage and a huge roar from the fans packed on to the pavement outside.
Police had to corral the crowds and shepherd the media from the main road as they gathered for the lunchtime verdict, crushed outside the court and clutching phones and touch pads to watch the announcement streamed live on the internet.
Some of the die-hard fans were in floods of tears as they celebrated the "relief" that "justice had been done".
The jury of seven men and five women took less than a day and a half of deliberations to find Conrad Murray guilty of involuntary manslaughter.
Murray was the man Michael Jackson entrusted as his personal doctor and the man who provided him with propofol - the anaesthetic drug he was using to get to sleep.
The die-hard Jackson fans will have nothing to do now the trial is over, after having gathered each day in tribute to the king of pop and taken part in a daily lottery for a seat in the public gallery.
But they'll be back at the end of the month when Dr Murray will appear again for sentencing - he faces a maximum of four years in jail.
Dr Murray was remanded in custody without bail until he receives his sentence, set for 29 November.
Explaining his decision, the judge said Dr Murray was now a convicted felon and had considerable ties outside the state of California, meaning he could not guarantee that the doctor would remain in the state.
Dr Murray sat silently in court, shifting slightly in his seat as the verdict was read out.
Court officers began to handcuff the physician as the judge made his final announcements, before leading him away into custody.
The jury - made up of one African American, six whites and five Hispanics - deliberated on Friday and through the morning on Monday.
Outside the court, fans of Michael Jackson were cheering and chanting, "Guilty! Guilty!" in the run-up to the verdict being announced.
During the six-week trial, 49 witnesses and more than 300 pieces of evidence were presented to the court.
Michael Jackson, who had been out of the public eye for several years, died in 2009 as he was preparing for a series of comeback performances at the O2 arena in London.
In his closing argument last Thursday, the prosecution said Dr Murray had caused the star's death through negligence, depriving Jackson's children of their father and the world of a "genius".
LA District Attorney Steve Cooley said the verdict sent a strong message
The defence argued that Jackson was a drug addict who caused his own death by giving himself an extra dose of propofol while the cardiologist was out of the room at the star's rented mansion in Los Angeles.
However, lawyers for Dr Murray dropped a key argument midway through the trial - that the pop superstar had drank the propofol. But they continued to argue that Jackson had somehow dosed himself otherwise.
Each side of the trial called their own expert witness on the anaesthetic drug,
There is no law against administering propofol, but the prosecution's case rested on the argument that Dr Murray was grossly negligent by doing so outside a hospital setting and without the proper monitoring equipment.
In some of the more shocking moments of the trial, the jury heard a recording of Jackson, sounding incoherent and slurred, speaking about his upcoming concert series, as well as viewing a photo of a lifeless Jackson on a gurney.