Kelly Thomas died at the hospital five days after a confrontation with police on July 5, 2011. Officers claimed they thought he was breaking into a car.
There are 119 potential jurors, so the jury selection process could take some time.
Manuel Ramos, 39, is charged with second-degree murder and involuntary manslaughter. Jay Cicinelli, 41, is charged with involuntary manslaughter and assault under color of authority. Both men were in court for jury selection.
The two defendants and a third officer, Joe Wolfe, allegedly held Thomas down and beat him with fists and a Taser gun. The 30-minute confrontation was caught on surveillance cameras. The defense says the officers were just doing their job.
Thomas, a homeless man with schizophrenia, was later cleared of any wrongdoing.
Judge said told the potential jurors that they would not be sequestered during the possible five-week trial, and many looked visibly relieved because the trial will happen over the holidays.
Ramos faces 15 years to life in prison if convicted, while Cicinelli faces four years if convicted. All three defendants have pleaded not guilty.
"This is the first time in Orange County's history on-duty officers have been charged with murder, and now they're finally going to trial for it," said Ron Thomas, Kelly's father.