Constance Marten and Mark Gordon have been charged with gross negligence manslaughter after the remains of a baby were found in a wooded area in England.
The Crown Prosecution Service said the aristocrat and her partner were also accused of concealing the birth of a child and perverting the course of justice.
An infant’s remains were found on Wednesday after a major two-day search operation in Sussex.
Marten, 35, and Gordon, 48, were arrested on Stanmer Villas in Brighton on Monday after avoiding the attention of police for several weeks.
On Thursday, the Metropolitan Police said it is “too early” to provide a specific date of death, adding that the infant had been dead for “several weeks”.
The pair are due to appear at Brighton Magistrates’ Court on Friday.
Barry Hughes, chief crown prosecutor for CPS London North, said: “The CPS has authorised the Metropolitan Police to charge Constance Marten and Mark Gordon with gross negligence manslaughter.
“Constance Marten, aged 35, and Mark Gordon, aged 48, have also been charged with concealing the birth of a child and perverting the course of justice.
“These charges arise from their arrest on Monday as a result of a lengthy police investigation to establish their whereabouts and that of their baby.
“The Crown Prosecution Service reminds all concerned that criminal proceedings against Constance Marten and Mark Gordon are active and that they have the right to a fair trial.”
The Met said a post-mortem examination would take place on Friday.
Earlier on Thursday, the force’s Detective Superintendent Lewis Basford said officers had been unable to determine the baby’s gender.
He told reporters the case had been referred to the police watchdog.
He said: “At this stage we have not yet been able to confirm the baby’s gender and post-mortem examination has not yet taken place.
“Despite this, based on our inquiries we’ve carried out so far, we believe sadly the baby may have been dead for some time before they were found.
“It is too early for us to provide a more specific date.
“Because we believe the death occurred during the course of a missing person investigation we have made a mandatory referral to the Independent Office for Police Conduct (IOPC).”
The IOPC said in a statement that it is “currently assessing the referral to determine what, if any, further action is required from us”.
