Biography:

Duff practiced law in Pittsburgh for thirty-six years, establishing the law firm of Duff, Scott and Smith.He also served as solicitor of Carnegie, and was an elector for Theodore Roosevelt in the 1912 presidential election. In addition to practicing law, Duff was engaged in the oil business for several years. He began by buying an oil driller's rig and taking a lease on some property about five miles from his home, where he struck oil. He subsequently engaged in ventures in other parts of western Pennsylvania as well as Mexico. He also served as president of the Criterion Oil Company and of the Westmoreland Natural Gas Company. He lost his fortune in the 1929 stock market crash, taking several years to recover financially. He was a delegate to the Republican National Convention in 1932, 1936, and 1940.

Duff was appointed Attorney General of Pennsylvania by Governor Edward Martin in 1943, serving in that position until 1947. During his tenure, he worked to strengthen the state's anti-stream pollution law despite facing strong opposition from the coal industry. He also fought against the mining industry after promoting legislation to prevent the discharge of mine silt into the Schuylkill River.
In 1946, Governor John Bell, who had been elected Lieutenant Governor in 1942 and had ascended to the governorship following Martin's resignation, declined to be a candidate in the gubernatorial election. Duff subsequently won the Republican nomination, and was elected the 34th Governor of Pennsylvania in the general election. His campaign focused on the issues of conservation, public health, and education. He handily defeated his Democratic opponent, former President pro tempore of the State Senate John Rice, by more than 557,000 votes.
Duff was elected to the United States Senate from Pennsylvania in 1950. After losing the 1956 election to Democrat Joe Clark in one of the closest elections in Pennsylvania history, Duff retired from politics, but remained in Washington, D.C. as a partner in the law firm of Davies, Richberg, Tydings, Landa & Duff. He died in Washington, D.C., and was buried in Carnegie, Pennsylvania.