Czolgosz was born in Detroit, Michigan, in 1873, the son of Polish immigrants.He was an unemployed factory worker and was living with his family in 1901. Czolgosz became interested in anarchism in the years preceding the McKinley murder. In May 1901 he attended a speech given by renowned anarchist Emma Goldman, in Cleveland, Ohio. Czolgosz traveled to Goldman's home in Chicago on July 12 and spoke briefly to Goldman before she left to catch a train. Goldman was later arrested and briefly detained on suspicion of involvement in McKinley's murder.

In his September 7 statement, Czolgosz said that he had read eight days prior, in Chicago, that McKinley would be attending the Exposition. He immediately took a train to Buffalo and found lodgings in a boarding house. Czolgosz attended the fair on September 5 for President's Day and heard McKinley's speech. He was tempted to shoot the President then but he could not get close enough. Instead, he returned to the Exposition the next day. Goldman's speech from May was still "burning him up". He joined the line of people waiting to shake the president's hand. Czolgosz wrapped his hand in a white handkerchief to hide the gun he was carrying. Secret Serviceman George Foster later explained his failure to observe Czolgosz's wrapped-up hand by saying that Czolgosz was too closely bunched up to the man in front of him.

The William McKinley assassination occurred on September 6, 1901, McKinley initially appeared to be recovering from his wounds, but took a turn for the worse six days after the shooting and died on September 14, 1901. Theodore Roosevelt succeeded McKinley as President. McKinley was the third of four U.S. presidents to be assassinated, following Abraham Lincoln in 1865 and James A. Garfield in 1881 and preceding John F. Kennedy in 1963. After McKinley's murder, Congress officially charged the Secret Service with the physical protection of U.S. presidents