The pleas came as part of a surprise deal with prosecutors that will spare victim Jaycee Dugard and her two daughters born after she was raped by defendant Phillip Garrido from having to testify at a trial.
The family had been kept in a hidden compound of backyard tents and sheds, never attending school or receiving medical attention.
Phillip Garrido, 60, faces a maximum sentence of 431 years to life in prison after entering guilty pleas to 14 kidnapping and sexual assault charges.
His wife, Nancy Garrido, 55, who originally faced the same charges as her husband, pleaded guilty to one count of kidnapping and one count of rape.
She faces a maximum sentence of 36 years to life. She is technically eligible for parole, but El Dorado County District Attorney Vern Pierson said it was "extraordinarily unlikely" she would ever be released from prison.
Pierson said the plea deal was only possible because Dugard, now 30, was willing to testify about her experiences in captivity.
He said he spoke with her on Wednesday night, and she remained willing to take the witness stand but was reluctant to put her children, now 13 and 16, through the ordeal.
"Frankly, I'm relieved that this means that that will not happen," Pierson said. "Should her children be called and drug into all of this was something that I don't think any mother in her right mind would want to see."
Both defendants waived their right to appeal and were scheduled to be sentenced on June 2.
The guilty pleas came at a hastily arranged court hearing after both defendants pleaded not guilty earlier this month.
Attorney Stephen Tapson, who represents Nancy Garrido, said outside court Thursday that both defendants agreed to change their pleas Wednesday.
The move came after prosecutors said they would drop some charges against Nancy Garrido if Phillip Garrido pleaded guilty to almost the full indictment, Tapson said.
Nancy Garrido feels terrible about what happened to Dugard, the lawyer said.
"She obviously committed a serious wrong, but in her view now, she's made peace with God and wants to get on with life, what's left of it," he said. "From the get-go she said, 'just do the best you can, Mr. Tapson, because I don't want to put Jaycee and the kids through a trial.'"
Dugard was snatched from her family's South Lake Tahoe street in June 1991 while walking to a school bus stop.
The case attracted international attention after Dugard surfaced in August 2009. Authorities said she and her children - fathered by Phillip Garrido and delivered by Nancy Garrido - had lived in the Garridos' backyard in Antioch.
They were discovered in August 2009 when authorities said Phillip Garrido took them to a meeting with his parole officer.
Dugard has been reunited with her mother and remained in Northern California with her and her daughters. She requested privacy and has not attended any of the court hearings. She is writing her memoirs, which are expected to be published in September.
Dugard's case revealed problems with California's system for monitoring convicted sex offenders after it was determined parole agents had missed numerous clues and chances to find her.
The Associated Press as a matter of policy avoids identifying victims of sexual abuse by name in its news reports
However, Dugard's disappearance had been known and reported for nearly two decades, making impossible any effort to shield her identity when she resurfaced.