Butte County District Attorney Michael L. Ramsey said the "historic moment" should be a signal that corporations will be held responsible for "recklessly endangering" lives.
The 84 people "did not need to die," Ramsey said. He said the deaths were "of the most unimaginable horror, being burned to death."
Before sentencing, survivors will testify Wednesday about the losses of their loved ones.
No individuals will be sent to prison, Ramsey said.
"This is the first time that PG&E or any major utility has been charged with homicide as the result of a reckless fire. It killed a town," Ramsey said, referring to Paradise, which was annihilated by the blaze.
According to court documents filed in March, the company will be fined "no more than $3,486,950," and it must reimburse the Butte County District Attorney's Office $500,000 for the costs of its investigation into the blaze.
Among other provisions, PG&E must establish a trust, compensating victims of the 2018 Camp Fire and other wildfires to the tune of $13.5 billion, according to the plea agreement included in a regulatory filing.
It has to pay hundreds of millions to the town of Paradise and Butte County and cooperate with prosecutors' investigation, the plea deal says.
PG&E also waived its right to appeal the case.
"I have heard the pain and the anguish of victims as they've described the loss they continue to endure, and the wounds that can't be healed," PG&E Corporation CEO and President Bill Johnson said after the plea. "No words from me could ever reduce the magnitude of such devastation or do anything to repair the damage. But I hope that the actions we are taking here today will help bring some measure of peace."
Johnson was in court Tuesday, where Butte County Superior Court Judge Michael Deems read the names of each victim as their photos were shown on a screen, CNN affiliate KTLA reported.
Johnson said the utility would never put profits ahead of safety again. He told the judge that PG&E took responsibility for the devastation "with eyes wide open to what happened and to what must never happen again," KTLA reported.
In March, the utility and the state agreed to bankruptcy terms, which included an overhaul of PG&E's board selection process, financial structure and oversight.
According to investigators with the California Department of Forestry and Fire Protection, PG&E was responsible for the devastating Camp Fire.
Electrical lines owned and operated by PG&E started the fire November 8, 2018, CAL Fire said in a news release.
"The tinder dry vegetation and Red Flag conditions consisting of strong winds, low humidity and warm temperatures promoted this fire and caused extreme rates of spread," CAL Fire said.
PG&E had previously said it was "probable" that its equipment started the Camp Fire but that it wasn't conclusive whether its lines ignited a second fire, as CAL Fire alleged.
The power company filed for bankruptcy in January 2019 as it came under pressure from billions of dollars in claims tied to deadly wildfires.