Mark Gordon and Constance Marten have both been found guilty of gross negligence manslaughter.
Marten, 38, and Gordon, 51, both denied the charges at the Old Bailey following the death of their child, Victoria.
Victoria died in a tent in the South Downs in January 2023, with her body recovered two months later.
There had been a high-profile police search for the missing baby, which culminated in the couple’s arrests in Brighton in February 2023 after 54 days on the run across England.
More than 1,000 Metropolitan Police officers were involved in the search before she was discovered in an allotment shed wrapped in a pink sheet and hidden beneath dirt and rubbish in a Lidl bag.
Victoria’s remains were too badly decomposed to establish the cause of death.
She likely died from hypothermia in the cold and damp conditions or was smothered, the prosecution said.
The couple left home with their young daughter after their four other children were taken into care.
Constance Marten, who is from a wealthy family, and her convicted rapist partner were convicted of perverting the course of justice, concealing the birth of a child and child cruelty in their first trial last year.
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Constance Marten and Mark Gordon found guilty on two counts PAFollowing the results of the re-trial, Detective Superintendent Lewis Basford of Scotland Yard, said: “Today, the justice we have long fought for has been finally been served for baby Victoria.
“The selfish actions of Mark Gordon and Constance Marten resulted in the death of a newborn baby who should have had the rest of her life ahead of her.”
Victoria's death was described as "completely avoidable" by Basford, who said the defendant had plenty of opportunities to "do the right thing" and ask for help.
Marten’s four other children have been taken into care.
Footage of Constance Marten holding baby Victoria under her coat outside Special Connection in East Ham, London
Metropolitan Police
Detective Chief Inspector Joanna Yorke, who led the homicide investigation into Victoria's death, said: "The selfish actions of Mark Gordon and Constance Marten resulted in the death of an innocent newborn baby who would have recently had her second birthday and should have had the rest of her life ahead of her.
"This was an incredibly challenging investigation for the hundreds of officers across the UK who were involved in the search.
"Our main focus throughout the search was finding Victoria alive and we were devastated by the outcome.
"We know today's verdict won't bring Victoria back, but I am pleased our investigation has resulted in the couple who caused her death finally being brought to justice."
Marten and her partner Mark Gordon have been found guilty at the Old Bailey of the manslaughter of their newborn baby
Metropolitan Police
In a police interview, Marten said: "I had her in my jacket and I hadn’t slept properly in quite a few days and erm, I fell asleep holding her sitting up and she, when I woke up, she wasn’t alive.”
The couple, who both gave evidence in their re-trial, had no response and refused to stand up as the verdict was read out.
In 1989, Gordon, then aged 14, held a woman against her will in Florida for more than four hours and raped her while armed with a “knife and hedge clippers”.
He was convicted of another offence involving aggravated battery and sentenced to 40 years in jail, and was released after 22 years.
The Lidl bag in which baby Victoria was found
Metropolitan Police
Following his release, Gordon was convicted of assaulting two female police officers at a maternity unit in Wales where Marten gave birth to their first child under a fake identity.
The pair kept the birth of Victoria, on Christmas Eve 2022, a secret from the authorities, going on the run across the UK.
Police tracked the pair from Wales to Bolton, where police found a placenta inside their abandoned car, prompting a major police alert.
Marten and Gordon travelled from the North West to Harwich in Essex, East Ham in London and on to Newhaven, spending hundreds of pounds on taxis.
Constance Marten holding baby Victoria under her coat outside Special Connection in East Ham, London
Metropolitan Police
Victoria was only briefly glimpsed on CCTV footage in London wearing the same teddy bear motif baby grow, later recovered with her body inside the Lidl bag.
The very young child was kept hidden under Marten’s jacket or inside the supermarket bag without adequate clothing.
The defendants were arrested after buying supplies in Brighton on February 27 2023.
They refused to say where Victoria was, with Gordon declaring: “What’s the big deal?”