Nellie May Madison was born on April 5, 1895, in Beaverhead County, Montana. She grew up in the town of Dillon. From a young age, she was trained as a survivalist, learning how to live off the land in the mountains of her home state. This knowledge would shape her early life and skills.

At the age of 13, Nellie faced a significant life change when she annulled her marriage to a 23-year-old man who had been in prison. This early experience was unusual for someone her age. Later in her life, she would marry three more times and also go through three divorces. Despite these relationships, Nellie had no children.

On March 24, 1934, in Burbank, California, Nellie May Madison shot her husband, Eric Madison. This happened after a series of alleged spousal abuse incidents. Nellie pointed a gun at Eric while he was changing clothes. He then reached under the bed for a box of butcher knives and threatened her. As he did this, Nellie shot him in the back five times, causing his death.

After the shooting, Nellie was arrested and put on trial for murder. The Los Angeles County District Attorney, Buron Fitts, sought the death penalty for her. During the trial, Nellie's lawyers advised her not to mention the abuse she had suffered. Instead, she claimed she was not at the scene when the murder took place. The jury found her story unbelievable, leading to her conviction. Judge Charles Fricke sentenced her to death, which the California Supreme Court later upheld.

Following her sentencing, Nellie's ex-husband advised her to speak out about the abuse. However, Judge Fricke dismissed her claims of domestic violence. Over time, Nellie gained public support, especially from journalist Agness "Aggie" Underwood. Underwood discovered that Eric had physically harmed not only Nellie but also his ex-wife. He had made them sign confessions about infidelity, while Eric himself had been unfaithful with underage girls.

The jurors who convicted Nellie later petitioned Governor Frank Merriam to reduce her sentence. In September 1935, he commuted her death sentence to life in prison. After writing many letters from prison, Governor Culbert Olson released her on March 27, 1943, nine years after the murder.

After her release, Nellie moved to San Bernardino and married her sixth husband, John Wagner, a house painter. This marriage lasted the longest of any she had. Nellie Madison died on July 8, 1953, due to a stroke.