The news comes four days after prosecutors publicly rejected an offer by the defense that Holmes would plead guilty to avoid execution.
"For James Eagan Holmes, justice is death," said District Attorney George Brauchler in court.
The former neuroscience graduate student is charged in the shooting rampage that killed 12 people and wounded 70 others during a midnight screening of "The Dark Knight Rises."
Prosecutors said last week that the defense proposal wasn't a valid plea bargain offer. They could still agree to a plea before the case goes to trial. After the death penalty announcement, Holmes' father nodded his head and put his arm around his wife, while relatives of victims cried.
Brauchler said before his decision, he spoke with relatives of 60 victims who died or were injured in the attack. According to ABC News sources, family members are divided on whether Holmes should get death. Some say they don't want to endure a trial.
"It could be 10 or 15 years before he's executed. I would be in my 40s and I'm planning to have a family, and the thought of having to look back and reliving everything at that point in my life, it would be difficult," said Pierce O'Farrill, who was shot three times.
Defense attorneys are expected to argue he is not guilty because he was legally insane at the time of the July 20 shooting. They balked at entering that plea last month, saying they couldn't make such a move until prosecutors made a formal decision on the death penalty.
ABC News and The Associated Press contributed to this report.
