Pacific Gas and Electric Co. will plead guilty to 85 felony counts because of its responsibility for the deadly 2018 Camp Fire, a monumental step that will mark one of the greatest corporate admissions of criminal liability in United States history.

PG&E Corp., the utility’s parent, revealed its plea agreement in a filing with the Securities and Exchange Commission on Monday. The company reached the agreement with Butte County District Attorney Mike Ramsey, who investigated the San Francisco company’s role in California’s deadliest and most destructive wildfire more than 16 months ago.

PG&E will admit to 84 counts of involuntary manslaughter and one count of unlawfully causing a fire, with three “special allegations” for greatly injuring a firefighter, greatly injuring more than one person and burning multiple structures.

No current or former PG&E executives were indicted because the liability did not rest with any one person, Ramsey said.

A PG&E power line started the Camp Fire, which destroyed nearly 19,000 buildings and almost totally leveled the town of Paradise. PG&E is already a convicted felon because of charges that arose from the deadly 2010 San Bruno gas pipeline explosion.

As part of the Butte County plea agreement, PG&E has agreed to pay a fine of about $3.5 million — the maximum allowed by law — and $500,000 to reimburse Ramsey’s office. The company will also spend as much as $15 million to provide water to Butte County residents who lost access as a result of damage to the Miocene Canal in the fire.

A Butte County grand jury indicted the company last week, forcing PG&E to choose whether it wanted to fight the matter at a trial.

“We decided to take responsibility for the role our equipment played in this fire,” said PG&E Corp. CEO Bill Johnson in an interview with The Chronicle. “We didn’t make this decision lightly, but in the end, I think this is the best course forward, particularly for the victims.”

Johnson said he hopes the plea “helps move along the process of rebuilding the communities and taking care of victims.”

PG&E’s plea agreement still needs to be entered in Butte County Superior Court and approved by the judge overseeing the company’s bankruptcy case. Both the utility and PG&E Corp. filed for bankruptcy protection in January 2019 because of their legal burden from the Camp Fire, the 2017 Wine Country wildfires and the 2015 Butte Fire.

Johnson was originally expected to appear in Butte County court on Friday, when PG&E would enter its plea, the district attorney’s office said in a statement. But the courthouse is closed because of the coronavirus pandemic, so PG&E is now scheduled to appear in court on April 24.

The 16-member grand jury that indicted PG&E was impaneled in March 2019 and had one year to complete its work, according to Ramsey’s office. Jurors “carefully listened to nearly 100 witnesses, examined over 1400 exhibits and produced many thousands of pages of transcript,” Ramsey said in his office’s statement.

The official Camp Fire death toll is 85 people. But Ramsey’s office said that “during the subsequent investigation more information was developed which cast doubt that one of those deaths was a direct result of the Camp Fire.”

PG&E’s agreement to plead guilty to involuntary manslaughter is a rare event for the U.S. legal and corporate systems.

Perhaps the closest recent analogue is BP, the petroleum company that pleaded guilty to 11 counts of manslaughter in 2012 over the 2010 Deepwater Horizon explosion that killed 11 people and sent millions of gallons of oil flowing into the Gulf of Mexico.

Ramsey told The Chronicle that PG&E’s 84-count involuntary manslaughter plea “seems to be unprecedented,” based on his office’s research and consulting with others.

“We’re not taking any victory laps, we’re just grateful that we have sought and hopefully obtained justice,” he said.

The pleading won’t fully heal the emotional scars still felt by the families of the victims, including Art Castile, whose partner is the stepdaughter of Camp Fire victim Bill Godbout.

“It doesn’t bring (Bill) back, and no one goes to jail,” Castile said, still saddened by the loss.

The news also was little consolation for Olivia Carmin, whose sister, Matilde Heffern, 68, died in the Paradise home she shared with her daughter, Christina, 40, and granddaughter, Ishka, 20.

“It does help a little,” Carmin, who lives in Georgia, said. “So many lost so much. I’m happy that PG&E has finally admitted that it was manslaughter. That is — I guess — a small win so far. But we lost so much when my sister died. It’s still sad.”

PG&E is serving its fourth of five years’ probation resulting from felony convictions that stem from the 2010 San Bruno gas pipeline explosion, which killed eight people and destroyed 38 homes. By admitting it committed felonies in connection to the Camp Fire, PG&E is in apparent violation of the terms of its probation from the San Bruno case.

Kelly Strader, a professor at Southwestern Law School, said in an email that the Camp Fire plea deal “may make sense for both sides.” The involuntary manslaughter charges “would have been hard to prove at trial, and the plea let the state proclaim victory without facing a challenging trial,” Strader said.

“For PG&E, the plea certainly is awful public relations, but it may well have decided that facing (involuntary manslaughter) charges would have been worse,” Strader said.

The Camp Fire began after a worn hook on PG&E’s 115,000-volt Caribou-Palermo transmission line failed on Nov. 8, 2018, state officials have concluded. The hook supported live power lines and it was attached to a century-old lattice steel electrical tower.

When the hook broke, power lines slapped against the tower, causing sparks to fly into the vegetation below, investigators say. Fast winds sent the flames racing toward Paradise, a town of about 20,000 people in the Sierra Nevada foothills east of Chico.

PG&E has been facing political threats to radically reshape its structure, including a bill by state Sen. Scott Wiener, D-San Francisco, that would put the company under the control of a new government agency.

PG&E has resisted those efforts. But as part of its bankruptcy, the company recently reached an agreement with Gov. Gavin Newsom that says PG&E could be bought by the state if it does not meet certain deadlines or if its operating license is revoked by regulators.

PG&E’s role in recent horrific fires has also prompted action from its state regulators at the California Public Utilities Commission.

In February, a commission administrative judge moved to impose a record $2.14 billion penalty against PG&E over the 2017 and 2018 wildfires. The penalty has not yet been finalized. Staff at the commission who investigated PG&E’s connection to the Camp Fire found that the company did notproperly maintain and inspect the equipment involved in the fire and botched an opportunity to prevent the disaster.

PG&E is appealing the judge’s decision, hoping to secure a lower penalty the company previously negotiated with commission staff and other groups.

More than a year after the Camp Fire, Christina Taft still finds herself missing her mother, Victoria. The 66-year-old former actress and Hollywood stuntwoman died in the fire after refusing to leave the Paradise duplex where she lived with her daughter.

Hearing about PG&E’s criminal charges wouldn’t bring her mother back — but it did help absolve Christina’s guilt. In the months after the wildfire, she blamed herself for Victoria’s‘ death.

“It’s very important for it to be criminal because a lot of the time it felt to me that no one was taking responsibility for the fire,” she said. “It helps the guilt and shame. When it came down to push and shove, during this huge fire that I had no control over, it felt like I did the wrong thing when I could have saved my mom. The Camp Fire should be looked as something that could have been prevented.”

San Francisco Chronicle staff writer Bob Egelko contributed to this report.

J.D. Morris and Lizzie Johnson are San Francisco Chronicle staff writers. Email: jd.morris@sfchronicle.com, ljohnson@sfchronicle.com Twitter: @thejdmorris, @lizziejohnsonnn