The vow - which is signed with blood - can be seen in his published diary, ‘From Albion To Shangri-La'.
Peaches, who was 19 years old when the vow was made, wrote: “I solemnly swear I am not going to die.”
Underneath, her name is written in blood, however the book’s publishers Thin Man Press cannot confirm whether this Peaches’ blood or the singer’s.
Peter’s own battle with addiction is well documented, and he has previously exhibited art created with his own blood.
Peaches died in April 2014, following a long battle with heroin addiction. An inquest held last week concluded that the mother-of-two’s death was the result of a heroin overdose.
Her husband Thomas Cohen told the inquest that Peaches had been receiving treatment for addiction and was taking weekly drug tests. He added that Peaches always told him the tests were negative.
Peaches was found dead at her family home in Kent on 7 April, by her husband Thomas. In the hours before her death, Peaches posted a childhood snap of herself and her mother online, with the simple caption “Mum and me”.