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.
However, by February this year the mother-of-two had started using heroin 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 Kent, on April 7 this year.
Police later found 6.9g of "importation quality" heroin stashed in a black cloth bag inside a cupboard over a bedroom door with a purity of 61 per cent, worth between £350 and £550.
They also discovered a syringe with residue of heroin inside a sweet box next to the bed, and other drug paraphernalia including burned spoons, syringes and knotted tights throughout the home.
North West Kent Coroner Roger Hatch said her death had been drugs-related and heroin played a part. He told the hearing that, though she had struggled to come off methadone, by November 2013 Ms Geldof was 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 we have heard here today. I therefore find the death of Peaches Geldof was drug-related and I express my sympathy to her family."
Mr Cohen told the inquest 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 on April 6 but, after failing to get hold of her the next day, he and his mother returned to the home with Astala and found Ms Geldof's body.
She had been having drugs tests which she told her husband were negative but he was concerned she might be taking heroin again, the inquest heard. Mr Cohen said he had found a message on her phone in February suggesting she had returned to heroin use. Later he saw her retrieve drugs she had hidden in the loft of their home and flush them down the toilet.
Detective Chief Inspector Paul Fotheringham told the inquest 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 as tolerance levels go down.