1. The Catholic Church: The phrase is commonly used in the Catholic Church to refer to someone who is about to receive the last rites, or "Last Anointing". This ritual is often performed for people who are terminally ill or facing imminent death.
2. The 1990s book and movie: The phrase gained widespread popularity with the publication of Sister Helen Prejean's 1993 book, "Dead Man Walking: An Eyewitness Account of the Death Penalty in the United States". The book, later adapted into a 1995 film, told the story of Prejean's work with condemned inmates on death row, especially her relationship with a man named Elmo Patrick Sonnier. The phrase became associated with the idea of facing execution, often in a state of hopelessness or resignation.
3. Folklore and popular culture: The phrase itself is likely a result of a long history of people facing death. The simple, direct language would have resonated with those facing their own mortality. It's possible the phrase was used in a variety of contexts prior to its modern usage.
In conclusion:
While the exact origin of the phrase "Dead Man Walking" is unclear, it's likely a combination of its use in the Catholic Church, its popularization by Sister Helen Prejean's book and film, and a general sense of resignation and inevitability associated with death.