The 25-year-old journalist, model and television presenter had been taking the substitute drug methadone in the two and a half years before she died.
But by February this year the mother-of-two had started using again, her musician husband Tom Cohen told an inquest in Gravesend, Kent.
Mr Cohen found her slumped on a bed in a spare room at their family home in Wrotham, Kent, on April 7 this year.
Police later found 6.9g (0.24oz) of “importation quality” heroin stashed in a black cloth bag inside a cupboard over a bedroom door with a purity of 61%, worth between £350 and £550.
They also discovered a syringe containing residue of heroin inside a sweet box next to the bed, and other drug paraphernalia including burnt spoons, syringes and knotted tights throughout the property.
North West Kent Coroner Roger Hatch said Ms Geldof’s death had been “drugs-related” and heroin had played a part.
He told the hearing that, although she had struggled to come off methadone, by November 2013 Ms Geldof was found to be free of heroin and reducing her methadone.
Mr Hatch said: “It’s said that the death of Peaches Geldof-Cohen is history repeating itself but this is not entirely so.
“By November last year she had ceased to take heroin as a result of the considerable treatment and counselling that she had received.
“This was a significant achievement for her but, for reasons we will never know, prior to her death she returned to taking heroin, with the fatal consequences that we have heard here today.
“I therefore find that the death of Peaches Geldof was drug-related and I express my sympathy to her family.”
Mr Cohen told the inquest that he had gone to stay with his parents in south east London with the couple’s two sons, Astala, two, and one-year-old Phaedra, in the days leading up to his wife’s death.
She had seemed fine when he spoke to her on several occasions over the weekend, he told the hearing.
His father, Keith, had seen Ms Geldof when he dropped the younger child home to her and did not notice anything amiss.
Mr Cohen said he had last spoken to his wife at 5.40pm on Sunday April 6 but, after failing to get hold of her the next day, he and his mother returned to the property with Astala and found Ms Geldof’s body.
Her last known movements included posting a picture of herself with her mother Paula Yates on social networking site Instagram with the comment “me and my mum” and watching The Dog Whisperer TV show on YouTube.
The model had been having weekly drugs tests which she told her husband were negative but he became concerned that she might be taking heroin again, the inquest heard.
Mr Cohen told the inquest that he had found a message on Ms Geldof’s phone in February suggesting that she had returned to heroin use.
Later he witnessed how she retrieved drugs she had hidden in the loft of their home and flushed them down the toilet.
The heroin found at the property “far exceeded” the 26% purity usually found at street level, Detective Chief Inspector Paul Fotheringham told the hearing.
Mr Fotheringham told the inquest that forensic scientist Emma Harris found a high level of morphine in Ms Geldof’s blood, suggesting she died “shortly after taking heroin”.
In her report, Dr Harris said it is common for users who stop taking heroin and then start again to die because their tolerance levels go down.
She said: “Persons taking heroin on a regular basis develop a tolerance to the drug, and such individuals can use doses that would be toxic, or fatal, to people with no tolerance.
“However, tolerance to heroin and other opiate drugs appears to be lost fairly rapidly when users cease to use the drug, and deaths commonly occur in people who have previously been tolerant and have returned to using heroin.