Leon Frank Czolgosz was born on May 5, 1873, in Detroit, Michigan. He was the youngest of eight children in a Polish-American family. His father was Paul Czolgosz, and his mother was Mary Nowak. The family moved to Alpena, Michigan, in 1880.

When Leon was ten years old, tragedy struck the family. They were living in Posen, Michigan, when his mother died shortly after giving birth to Leon's sister, Victoria. In 1889, the family relocated to Natrona, Pennsylvania, where Leon began working at a glass factory.

At the age of 17, Czolgosz and his family moved to Cleveland, Ohio. He found a job at the Cleveland Rolling Mill Company. However, in 1893, the mill faced issues due to an economic crash. The mill closed for a time and tried to cut wages.

During this period of economic hardship, Czolgosz felt disillusioned with the Catholic Church and began looking for answers. He joined a working man's socialist club called the Knights of the Golden Eagle. Later, he became involved with a more radical group known as the Sila Club. This is where he developed an interest in anarchism.

In 1898, after witnessing several strikes that often ended in violence, Czolgosz faced health issues related to a respiratory disease. He decided to live with his father, who had recently bought a 50-acre farm in Warrensville, Ohio. During this time, Czolgosz became increasingly reclusive.

His life took a turn when he attended a lecture by the anarchist Emma Goldman in Cleveland in May 1901. After the lecture, he approached her to ask for book recommendations. He also met her again in July 1901, in Chicago. He expressed his disappointment with the local socialists and sought connections in the anarchist community.

Czolgosz's behavior raised suspicions among some anarchists, leading to warnings in their publications about him potentially being an informant. He believed that there was significant injustice in American society, feeling that the wealthy exploited the poor. Around this time, he learned of the assassination of King Umberto I of Italy, which further influenced his views on taking action against perceived injustices.

On August 31, 1901, Leon Czolgosz went to Buffalo, New York, to attend the Pan-American Exposition. He rented a room in a hotel and planned to kill President William McKinley, who was scheduled to speak there. On September 6, Czolgosz concealed a .32-caliber revolver and approached McKinley while the president was greeting the public inside the Temple of Music. At approximately 4:07 p.m., when McKinley reached out to shake his hand, Czolgosz shot him twice in the abdomen at close range.

The first bullet ricocheted off McKinley's coat button and did not penetrate. The second bullet seriously injured McKinley, lodging in his stomach. Although the wound was not instantly fatal, McKinley died eight days later from an infection caused by the bullet wound.

Immediately after the shooting, several people in the crowd tried to attack Czolgosz. One man managed to strike him in the neck and knocked the gun from his hand. Police intervened and took Czolgosz into custody at the local precinct. He was then moved to police headquarters for further processing.

Following McKinley’s death, Czolgosz was arraigned on charges of first-degree murder. A grand jury indicted him on September 16, 1901. During his trial, which began on September 23, Czolgosz did not call any witnesses to defend himself. He claimed to plead guilty, but the judge entered a not guilty plea on his behalf. The trial lasted only a few days, and the jury deliberated for less than half an hour before convicting him.

Czolgosz was sentenced to death and was executed by electric chair on October 29, 1901, just 45 days after McKinley died. His last words indicated he felt no regret for the assassination, stating he killed McKinley because he believed the president was the enemy of the working people. After his execution, his body was subjected to an autopsy, and his remains were disposed of in a way intended to prevent future public display.