James attended public schools in Carnegie and Princeton University, where he received a B. A. in 1904. After two years at the University of Pennsylvania Law School, he completed his law studies at the University of Pittsburgh and received an Bachelor of Laws in 1907.
Duff was an avid outdoorsman, and although he opened a law practice in Pittsburgh, he was attracted to the oil and gas fields of western Pennsylvania. Duff borrowed $5, 000 to buy an oil driller's rig, struck oil, and went on wildcat ventures in Texas and Mexico. He lost everything in the stock market crash of 1929 and returned to the full-time practice of law. These experiences left him unintimidated by men of great wealth. He held no elected office until he was sixty-three, but he was long active in Pennsylvania politics.
In 1912 Duff was a presidential elector for Theodore Roosevelt's Progressive party. Later he returned to the Republican party and served as its chairman for the Twelfth Legislative District in Pittsburgh and as a delegate to the Republican conventions of 1932, 1936, and 1940, when he actively supported Wendell Willkie. In 1943 Governor Edward Martin appointed him attorney general of the commonwealth. Duff used that post to draw attention to the pollution of Pennsylvania's rivers and streams, and he won enactment of protective legislation over the opposition of the coal industry.
In 1946 Governor Martin, constitutionally barred from succeeding himself, ran for the United States Senate. Republican factions headed by Joseph R. Grundy and Joseph N. Pew, frequently at odds with each other, met to choose a gubernatorial candidate acceptable to both sides. Duff agreed to run, and with the support of Grundy and Pew he won the governorship by a wide margin; he then began to establish his political independence. He also drew fire from organized labor by signing legislation that prohibited public-utility workers from striking. Once he dispersed striking truckers, who had used their vehicles to block the Pennsylvania Turnpike, by ordering the highway department to bulldoze the trucks off the road.
Duff's break with Grundy was sealed at the 1948 Republican National Convention. Duff worked for the nomination of Arthur Vandenberg, while the Grundy forces, including Senator Martin, threw their support behind Thomas E. Dewey. Routed at the convention, Duff confronted the Grundy machine directly when he ran against its candidate for the Republican senatorial nomination in 1950. Duff won the nomination by a landslide and went on to defeat the Senate Democratic whip, Francis Myers. Duff's victory was attributable to his progressive record as governor and to his popular personal style.
Duff arrived in the United States Senate with a reputation as "rough, tough Duff, " a no-holds-barred, bare-knuckle political fighter, but he found the adjustment to a legislative arena difficult. As governor, he had shunned cabinet meetings, met with department heads individually, and made decisions on his own. Now, as a sixty-seven-year-old freshman, he had only a small staff and minor committee assignments.
His relations with Senate Republican leaders Robert Taft and Kenneth Wherry were polite but cool, and he got along poorly with his conservative senior colleague, Ed Martin. Senate traditions also required junior members to keep silent during their first years. Consequently, Duff turned his energies to presidential politics and became a founder of the movement to draft Dwight D. Eisenhower. Duff swallowed his dislike of Dewey and met regularly with Dewey, Herbert Brownell, Henry Cabot Lodge, Hugh Scott, and other eastern internationalist Republicans who were determined to prevent the midwestern isolationist Robert Taft from receiving their party's nomination.
Duff built up support for Eisenhower and tore into those who opposed him. Lodge recalled that in 1951 Duff "virtually single-handedly kept the Eisenhower movement alive by going on a speaking tour and frequently saying printable things: and here and there a few unprintable things. " President Eisenhower owed Duff a great debt, but Duff rarely tried to collect on it. He made few patronage demands and seemed content with access to the White House. With the Republican victory in 1952, Duff received more-important assignments on the Armed Services and Commerce committees. He also spoke out against Senator Joseph R. McCarthy and voted in favor of censure of McCarthy.
But Duff's Senate term lacked notable achievement, and he was often absent during roll-call votes. Eisenhower's memoirs credit Duff with 100 percent support of administration programs in 1953, the only senator to achieve a perfect score, but in subsequent years the conservative Martin voted more in line with the administration than did Duff. Nevertheless, when Duff ran for reelection in 1956 Eisenhower campaigned for him as an exemplar of modern Republicanism. Duff's disenchantment with the Senate showed in his uninspired campaign. His opponent, Joseph Clark, the mayor of Philadelphia, toured with an empty chair representing Duff's absenteeism. The charge made Duff furious, but he could not refute it. In spite of Eisenhower's 600, 000-vote margin in Pennsylvania, Duff lost by 17, 900 votes, less than 1 percent of the total.
He retired from politics to his law practice, and he remained vigorous right up to the moment when he collapsed and died at Washington, District of Columbia.
Like Theodore Roosevelt, Duff enjoyed a good fight and saw politics as a bully pulpit. An independent, middle-of-the-road politician, he charted a course remarkably free of organized interests, either business or labor. He opposed "free government handouts" but believed that government should do for people what they could not do for themselves.
He cited Theodore Roosevelt, Woodrow Wilson, and Harry Truman as his political heroes because "they were willing to fight the trend if they believed in something else. " That description fit Duff himself.
"Any damn fool can make a million dollars. "
"If you think I'm going to give you a free seat in the grandstand at the same time I'm going to raise the price of bleacher seats, you're crazy. "
"I believe in keeping myself close to the average guy. "
Duff married Jean Kerr Taylor on October 26, 1909; they had no children