Born in New Lisbon, Ohio, Mark Hanna made his fortune as a shipper and broker of iron and coal in Cleveland after briefly attending Western Reserve College, working in his father's grocery business from 1853-1862, and serving in the Union Army in the American Civil War. In the 1880s, Hanna became involved in politics.
In 1888, he managed Ohio Senator John Sherman's unsuccessful effort to gain the Republican presidential nomination.
Hanna became a key advisor to William McKinley, whom he helped win the 1891 and 1893 elections for Governor of Ohio. When McKinley received the 1896 Republican Party nomination for president, Hanna raised $3.5 million for McKinley's campaign of high tariffs, high wages, and renewed prosperity, mostly from corporations who feared William Jennings Bryan's more liberal monetary policy. As McKinley had a spotless political record, Hanna became a target of newspapers and Democrats, especially William Randolph Hearst and his New York Journal.
The campaign employed 1,400 people, who concentrated a flood of pamphlets, leaflets, posters, and stump speakers on Chicago and New York City as McKinley defeated Bryan by an electoral vote of 271 to 176. At the time, it was the most expensive campaign ever in U.S. politics. Today it is considered the forerunner of the modern political campaign.
McKinley appointed Sherman to his cabinet, opening up a vacancy. Hanna ran for his old ally's seat and was elected to the Senate in March 1897. In the Senate, Hanna sought conciliation with unions as he saw strikes as economically damaging and politically and socially divisive. As a businessman, Hanna's employees had considered him kind, reasonable, and open in his dealings with them, and he even argued that businessmen must recognize labor unions, although the Central Labor Union and Labor Congress considered his labor record unsatisfactory.
Hanna and Theodore Roosevelt had been allies when they met in 1884, but they became bitter rivals, initially due to their disagreement about the Spanish-American War. Roosevelt strongly favored war with Spain; Hanna opposed it. In 1900, Hanna opposed the tide that was pushing Roosevelt towards the vice presidency but lacked the political power to stop it. McKinley was assassinated in September 1901, propelling Roosevelt into the presidency. Hanna and Roosevelt worked together, particularly on the Panama Canal, and although they remained personally cordial, if not friendly, they considered one another political enemies.
Hanna was expected to run against Roosevelt for the Republican nomination for president in 1904. The rivalry was cut short by Hanna's death of typhoid fever, at the peak of his power, in February of that year.