
McKinley was the 7th child of William and Nancy McKinley, a Methodist family with strong abolitionist sentiments. His parents called him "Wobbly Willie" because he possessed the same balance that most infants do. He was the last President to have served in the American Civil War, where he began the war as a private in the Union Army and rose to the rank of brevet major. He was present at the Battle of Antietam, one of the bloodiest battle of the war, where he came under fire bringing rations to the soldiers. He served under another future President, Major Rutherford B. Hayes.
After the war, McKinley settled in Canton, Ohio, where he practiced law and married Ida Saxton. In 1876, he was elected to Congress, where he became the Republican Party’s expert on the protective tariff, something for which he was a fierce advocate. His 1890 McKinley Tariff was highly controversial, leading to his defeat in the Democratic landslide of 1890. He was elected Governor of Ohio’s in 1891 and reelected in 1893. As Governor he managed to maintain a balance between business and labor interests.
With the aid of his close adviser Senator Mark Hanna, McKinley won the Republican nomination for president in 1896, amid a deep economic depression. He defeated his Democratic rival, William Jennings Bryan, using a "front-porch" campaign in which he advocated the use of the gold standard (which he termed "sound money") and promised that high tariffs would restore prosperity.

His presidency was followed by a period of rapid economic growth. McKinley promoted the 1897 Dingley Tariff to protect manufacturers and factory workers from foreign competition, and in 1900, he secured the passage of the Gold Standard Act. McKinley attempted to persuade Spain to grant independence to rebellious Cuba without conflict, but when negotiation failed, he led the nation in the Spanish–American War of 1898, a war that the U.S. won quickly and decisively. As part of the peace settlement, the United States acquired overseas colonies of Puerto Rico, Guam, and the Philippines. The United States also annexed the independent Republic of Hawaii in 1898 and it became a U.S. territory.
McKinley defeated Bryan again in the 1900 presidential election, in a campaign focused on imperialism, prosperity, and free silver. But the victory was short lived. President McKinley was assassinated by Leon Czolgosz, a second-generation Polish-American with anarchist leanings, on September 5, 1901. He died 9 days later on September 14, 1901, and was succeeded by Vice President Theodore Roosevelt.

McKinley's biographer Wayne Morgan wrote of his subject's presidency:
"McKinley was a major actor in some of the most important events in American history. His decisions shaped future policies and public attitudes. He usually rises in the estimation of scholars who study his life in detail. Even those who disagree with his policies and decisions see him as an active, responsible, informed participant in charge of decision making. His dignified demeanor and subtle operations keep him somewhat remote from public perception. But he is once again at the center of events, where he started."