He is thought to have been Britain's most prolific serial killer, with 218 victims generally seen as a conservative estimate.
But Shipman never admitted to a single crime, leaving most questions about his killings unanswered when he committed suicide in 2004.
During his incarceration, he wrote a total of 65 letters to two patients, husband and wife David and Mavis Stott, denying his guilt, mocking victim's families as fame-seekers and describing South Manchester coroner John Pollard, to whom the case was first brought, as a "moron" who was seeking his "glory days".
Pollard has now criticised the auction of the letters as "raking it up again" for the families, some of whom have also strongly criticised using the letters to generate profit.
MP for Stalybridge and Hyde, James Purnell has also expressed distaste at the sale.
Auctioneer Nick Hall's initial comment on the letters was to say: "This is an amazing discovery. They cover his whole life from his arrest to his eventual suicide and a fascinating glimpse into what this man was thinking."
Shipman was convicted of 15 murders in 2000.
He left no note to explain why he hanged himself in 2004, although he had commented to a guard that if he committed suicide before he was 60, his wife would receive a full NHS pension, which she did.
Both the Stotts have died since the letters were written, and their son discovered the letters when clearing out their home.
The letters are scheduled to be sold on November 10 in Knutsford, Cheshire, United Kingdom.