James Henderson Duff (January 21, 1883 - December 20, 1969) was an American lawyer and politician in the mid-20th century. He served as the Governor of Pennsylvania (1947-1951) and U.S. senator from Pennsylvania (1951-1957).
Duff was active in politics throughout his adult life, but did not become a political candidate until 1942, after 35 years as a partner in the Pittsburgh law firm of Duff, Scott & Smith. He successfully ran for Pennsylvania state attorney general, and took office in 1943. Four years later, he ran and won as the Republican candidate for governor.
After losing the 1956 senatorial election to Democrat Joseph S. Clark, Duff retired from politics, but remained in Washington, DC as a partner in the law firm of Davies, Richberg, Tydings, Landa & Duff. He died in Washington, DC, and was buried in Carnegie, Pennsylvania.
Duff was a native of Mansfield (now Carnegie), Pennsylvania. He received his bachelor's degree from Princeton University in 1904 and his law degree from the University of Pittsburgh in 1907. He married Jean Taylor on October 26, 1909.