Marcus Alonzo Hanna was born in New Lisbon, Ohio, on September 24, 1837. After his fathers death in 1862, he became a partner in the familys Cleveland wholesale grocery firm. Two years later, he married the daughter of coal and iron magnate Daniel P. Rhodes. He later joined his family firm to Rhodes business, and the new company was reorganized in 1885 as M. A. Hanna and Company. In addition, he held interests in other Cleveland businesses, including a bank, a newspaper, the Opera House and the street railway system. He contributed to the 1880 presidential campaign, which earned him a place on the Republican State Committee. He supported Congressman William McKinleys protectionist tariff of 1890, and aided him in his successful bid for the governorship of Ohio in 1891. Hanna helped McKinley win the Republican nomination for President in 1896, and managed McKinleys campaign, while serving as chair of the Republican National Committee.
Hanna rejected a cabinet post, but was appointed US Senator from Ohio in 1897 to replace John Sherman, who had moved on to the post of Secretary of State in McKinleys cabinet. In 1898, Hanna was elected to a full term. Initially opposed to interventionism and imperialism, Hanna eventually became a supporter of both policies. He also promoted the interests of big business, supported the Panama Canal, opposed civil service reform, and tried unsuccessfully to restore the failing merchant marine.
After McKinleys assassination, Hanna remained in Washington as an advisor to the new President, Theodore Roosevelt. In 1901, he was appointed chairman of the National Civic Federation, later helping settle the anthracite strike of 1902. Hanna died on February 15, 1904, in Washington, D.C.