Thomas Andrew Williamson was born on April 23, 1831, in Mackinaw Township, Illinois. He was one of five children in a wealthy farming family led by his father, Reuben W. Williamson. Thomas described his father as a strict man who expected hard work from him from a young age. As a child, Thomas began to show signs of trouble. At the age of 10, he started stealing and was known as a miscreant in Tazewell County. He often spent his evenings in Oakdale.

When he was 13 years old, Thomas attempted to rob a store in Pekin. He was caught and sent to the local penitentiary but was released after being found not guilty during a trial weeks later. At 22, he became ill and was paralyzed on one side. After his recovery, he alternated between working for his father and his uncle.

Thomas was jailed for horse stealing in Centralia when he was a young man. He spent a week in jail before being released. After this, he decided to join the Union Army, believing military life might be better for him. He enlisted in the 7th Illinois Infantry Regiment and spent most of his service time in Bald Knob. After his honorable discharge, he returned to Mackinaw Township, where he worked several odd jobs and earned a good income.

Later, Thomas enlisted in the 108th Illinois Infantry Regiment, which was sent to Tennessee. During his military service, he stole small items from fellow soldiers. He claimed to have fought in significant battles, including the Siege of Vicksburg and the Battle of Gettysburg. After the Civil War ended, he returned to Illinois.

In 1868, Thomas Andrew Williamson, along with his brother-in-law Shivler and a friend named Harket, went to the home of an elderly man named August Koch in Delavan. They played cards and drank heavily. An argument broke out when Koch accused them of cheating. In the heat of the moment, Williamson and his companions killed Koch and buried his body under the house. Eventually, Shivler and Harket were captured, but Williamson managed to evade arrest for a short time before being caught in Springfield. All three men received death sentences, but Governor Richard J. Oglesby commuted their sentences at the last minute, and Williamson spent 11 years in prison before being released in April 1879.

After his release, Williamson married Susan Kerk in Centralia, Missouri. They struggled financially and traveled around selling wares. By the fall of 1889, they were living in a log cabin six miles outside Sedalia, but soon after, Susan disappeared. Williamson claimed she went to visit relatives and later died from a health issue while in Illinois. He said he could not afford to bring her body back. Some people were suspicious, but no investigation was pursued. After Williamson left the cabin, Dan Clossier, the new owner, was told not to dig in a certain spot where Williamson claimed to have planted parsnips.

In early May 1890, Charles Moore disappeared from his father's farm, and soon after, his father, Jeff Moore, also went missing. Williamson was present when others began to inquire about the Moores' whereabouts, which raised suspicion. Local authorities were alerted to Williamson's state when he attempted suicide at Sicher's Park. After requiring medical assistance, he recovered. Meanwhile, a search party uncovered the buried bodies of Jeff and Charles Moore on their property, both showing signs of violence.

As suspicions mounted, Williamson was arrested to prevent a potential lynching. Following this, the remains of his wife were discovered in the log cabin where they had lived. A jury determined that all three victims had been murdered by Williamson, and he faced trial for their deaths.

While awaiting trial, Williamson admitted to killing the Moores but later claimed he had been hired to do so. During preliminary hearings, evidence was presented linking him to the murders, including a hat that matched one belonging to Charles Moore. Williamson was indicted on November 30, 1890. His trial commenced, and after two weeks, the jury found him guilty. He was sentenced to death, but his attorney attempted to appeal the decision.

Ultimately, the Supreme Court of Missouri upheld the conviction, and death by hanging was confirmed for October 31, 1891. On the day of his execution, Williamson walked to the scaffold, admitted to his crimes, and expressed no fear of dying. He was pronounced dead shortly after the trap was sprung. With no one to claim his body, Thomas Andrew Williamson was buried in a potter's field.