He subsequently entered elective politics and was eventually elected to the United States Senate from Kentucky; he has served there since 1999 as a Republican. He previously served in the U.S. House of Representatives representing Kentucky's 4th Congressional District from 1987 to 1999.

Jim Bunning graduated from St. Xavier High School in Cincinnati in 1949 and later received a bachelor's degree in economics from Xavier University.

Jim Bunning's first game as a major league pitcher was on July 20, 1955. He pitched for the Detroit Tigers from 1955 to 1963, moving to the Philadelphia Phillies from 1964 through 1967, to the Pittsburgh Pirates from 1968 through the middle of the 1969 season, finished the 1969 season on the Los Angeles Dodgers, and returned to the Phillies in 1970, retiring in 1971. He wore uniform number 15 on the 1955 Tigers, switched to 14 in 1956, which was the number he wore for the Tigers, Phillies, and Pirates until he was traded to the Dodgers in 1969. For the Dodgers, he wore number 17, but returned to number 14 on being returned to the Phillies. Bunning pitched his first no-hitter on July 20, 1958 for the Detroit Tigers against the Boston Red Sox. His second was a perfect game, which came against the New York Mets on June 21, 1964, Father's Day. He is one of only five players to throw a no-hitter in both leagues. He played in the All-Star Games in 1957, 1959, every year from 1961 through 1964, and in 1966. In 1996 he was elected to the Baseball Hall of Fame, via Veterans Committee. Currently, Jim has received the most votes cast by the BBWAA during the course of any and all player's Hall of Fame eligibility period collecting well over 3000 votes.

First elected to office in 1977, the ambitious Bunning would serve only two years on the city council of Fort Thomas, Kentucky before running for and winning a seat in the Kentucky Senate as a Republican. He was elected minority leader by his Republican colleagues, a rare feat for a freshman legislator.

Bunning was the Republican candidate for governor in 1983. He and his running mate Eugene P. Stuart lost in the general election to their Democratic opponents, Lieutenant Governor of Kentucky Martha Layne Collins and Attorney General Steve Beshear. Bunning won 454,650 votes (44.1%) to 561,674 (54.5%) for Collins.

In 1986, Bunning won the Republican nomination in Kentucky's 4th District, based in Kentucky's share of the Cincinnati metro area, after 10-term incumbent Gene Snyder retired. He won easily in the fall and was reelected five more times without serious opposition in what was considered the most Republican district in Kentucky. After the Republicans gained control of the House in 1995, Bunning served as chairman of the House Ways and Means Subcommittee on Social Security until 1999.

In 1998, Senate Minority Whip Wendell Ford decided to retire after 24 years in the Senate--the longest term in Kentucky history. Bunning won the Republican nomination for the seat, and faced fellow Congressman Scotty Baesler, a Democrat from the Lexington-based 6th District, in the general election. Bunning defeated Baesler by just over half a percentage point. The race was very close; Bunning only won by swamping Baesler in the 4th by a margin that Baesler couldn't make up in the rest of the state (Baesler barely won the 6th).

Among the bills that Bunning sponsored is the Bunning-Bereuter-Blumenauer Flood Insurance Reform Act of 2004. He is one of the Senate's most conservative members, gaining high marks from several conservative interest groups.

Bunning was also the only member of the United States Senate Banking and Urban Affairs Committee to have opposed Ben Bernanke for Chief of the Federal Reserve. He claimed it was because he had doubts that he would not be different from Alan Greenspan.

Bunning was heavily favored for a second term in 2004 after his expected Democratic opponent, Governor Paul Patton, saw his career implode in a scandal over an extramarital affair. Eventually, the Democrats settled on Daniel Mongiardo, a relatively unknown physician and state senator from Hazard.

During Bunning's reelection bid in 2004, controversy erupted when Bunning described Mongiardo as looking "like one of Saddam Hussein's sons." Public distaste compelled him to apologize. Other behavior, including accusing Mongiardo of physically assaulting Bunning's wife—claiming that his wife was left "black and blue"—and the accusation that he used a teleprompter during a televised debate caused several media analysts to question Bunning's mental state. Bunning set unprecedented conditions on the debate: he could not appear in person due to an important vote held just few hours before the debate and instead was televised from the Republican national headquarters; he refused to allow an independent observer in the room with him; he insisted that no portion of any recording of his performance could be rebroadcast; he insisted that the debate be broadcast live in the afternoon instead of the customary prime time hours; and other conditions.[1] After the debate, the state's two largest newspapers, the Louisville Courier-Journal and Lexington Herald-Leader, both called for Bunning to step down, however both papers had been strident Bunning opponents previously.

Bunning had an estimated $4 million campaign war chest, while Mongiardo had only $600,000. The Democratic Party began increasing financial support to Mongiardo when it became apparent that Bunning's bizarre behavior was costing him votes, purchasing more than $800,000 worth of additional television airtime on his behalf.

The race turned out to be very close, with Mongiardo leading with as many as 80% of the returns coming in. However, Bunning eventually won by just over one percentage point. Some analysts felt that had it not been for George W. Bush's 20-point victory in the state, Mongiardo would have won.

As was expected in light of Bunning's previous career as a baseball player, Bunning has been very interested in Congress's investigation of steroid use in baseball. Bunning has also been outspoken on the issue of illegal immigration taking the position that all illegal immigrants should be deported.

In April 2006, he was selected by Time as one of "America's Five Worst Senators." The magazine dubbed him "The Underperformer" for his "lackluster performance", noting he "shows little interest in policy unless it involves baseball", and criticized his hostility towards staff and fellow Senators and his "bizarre behavior" during his 2004 campaign.