Buckley was born November 24, 1925, in New York City, the son of Aloise Josephine Antonia (Steiner) and william Frank Buckley Sr., a Texas-born Lawyer and oil developer. His mother, from New Orleans, was of Swiss-German, German, and Irish descent, while his paternal grandparents, from Hamilton, Ontario, Canada, were of Irish ancestry. The sixth of ten children, Buckley moved as a boy with his family to Mexico, and then to Sharon, Connecticut, before beginning his formal schooling in Paris, where he attended first grade. By age seven, he received his first formal training in English at a day school in London; his first and second languages were Spanish and French. As a boy, Buckley developed a love for music, sailing, horses, hunting, and skiing. All of these interests would be reflected in his later writings. Just before World War II, at age 12–13, he attended the Catholic preparatory school St. John's Beaumont School in England.

William F. Buckley Jr. had nine siblings, including sister Maureen Buckley-O'Reilly (1933–1964) who married Gerald A. O'Reilly, the CEO of Richardson-Vicks drugs; sister Priscilla L. Buckley, author of Living It Up With National Review: A Memoir, for which william wrote the foreword; sister Patricia Buckley Bozell, who was Patricia Taylor's roommate at Vassar before each married; brother Reid Buckley, an author, debate-master, and founder of the Buckley School of Public Speaking; and brother James L. Buckley, who became a U.S. Senator from New York and was later a judge of the United States Court of Appeals for the D.C. Circuit. Buckley co-authored a book, McCarthy and His Enemies, with his brother-in-law, attorney L. Brent Bozell Jr. (Patricia's husband), who worked with Buckley at The American Mercury in the early 1950s when it was edited by william Bradford Huie. Buckley's oldest sister Aloise Buckley Heath was a Writer and conservative Activist.

Buckley was homeschooled through the 8th grade using the Calvert School of Baltimore's Homeschool Curriculum. Buckley attended the National Autonomous University of Mexico (or UNAM) in 1943. The following year upon his graduation from the U.S. Army Officer Candidate School, he was commissioned as a second lieutenant in the United States Army. In his book, Miles Gone By, he briefly recounts being a member of Franklin Roosevelt's honor guard upon the President's death. He served stateside throughout the war at Fort Benning, Georgia; Fort Gordon, Georgia; and Fort Sam Houston, Texas.

With the end of World War II in 1945, he enrolled in Yale University, where he became a member of the secret Skull and Bones society and was a masterful debater. He was an active member of the Independent Party of the Yale Political Union, and also served as Chairman of the Yale Daily News and as an informer for the FBI. Buckley studied political science, history, and economics at Yale, graduating with honors in 1950. He excelled on the Yale Debate Team, and under the tutelage of Yale professor Rollin G. Osterweis, Buckley honed his acerbic style.

Buckley worked as an Editor for The American Mercury in 1951 and 1952, but left after perceiving newly emerging anti-Semitic tendencies in the magazine.

In 1953–54, long before he founded Firing Line, Buckley was an occasional panelist on the conservative public affairs program Answers for Americans broadcast on ABC and based on source material from the H. L. Hunt–supported publication Facts Forum.

In 1954, Buckley co-wrote a book, McCarthy and His Enemies, with his brother-in-law L. Brent Bozell Jr. that strongly defended Senator Joseph McCarthy as a patriotic crusader against communism.

Buckley founded National Review in 1955 at a time when there were few publications devoted to conservative commentary, serving as editor-in-chief until 1990. During that time, National Review became the standard-bearer of American conservatism, promoting the fusion of traditional conservatives and libertarians.

James Jackson Kilpatrick (1920–2010) was a well-known newspaper Editor in Richmond, Virginia, who was a leader in supporting segregation and the control of the South by whites only. MacLean states: "The National Review made Kilpatrick its voice on the civil rights movement and the Constitution, as Buckley and Kilpatrick united North and South in a shared vision for the nation that included upholding white supremacy." In the August 24, 1957, issue, Buckley's editorial "Why the South Must Prevail" spoke out explicitly in favor of temporary segregation in the South until "long term equality could be achieved". It argued that "the central question that emerges ... is whether the White community in the South is entitled to take such measures as are necessary to prevail, politically and culturally, in areas where it does not predominate numerically? The sobering answer is Yes—the White community is so entitled because, for the time being, it is the advanced race." His answer was that temporary segregation in the South was a good idea now (in 1957) and the black population lacked the education, economic, or cultural development for racial equality to be possible, claiming the white South had "the right to impose superior mores for whatever period it takes to effect a genuine cultural equality between the races". Two weeks after that editorial was published, another prominent conservative Writer, L. Brent Bozell Jr. (Buckley's brother-in-law), wrote in the National Review: "This magazine has expressed views on the racial question that I consider dead wrong, and capable of doing great hurt to the promotion of conservative causes. There is a law involved, and a Constitution, and the editorial gives White Southerners leave to violate them both in order to keep the Negro politically impotent."

In the late 1960s, Buckley joined the Board of Directors of Amnesty International USA. He resigned in January 1978 in protest over the organization's stance against capital punishment as expressed in its Stockholm Declaration of 1977, which he said would lead to the "inevitable sectarianization of the amnesty movement".

In 1962, the convicted murderer Edgar Smith began a correspondence with Buckley during which Buckley began to doubt Smith's guilt, later stating that the case was "inherently implausible".

In 1963–64, Buckley mobilized support for the candidacy of Arizona Senator Barry Goldwater, first for the Republican nomination against New York Governor Nelson Rockefeller and then for the Presidency. Buckley used National Review as a forum for mobilizing support for Goldwater.

The Buckley Rule is often misquoted. william F. Buckley first used his assertion during the 1964 Republican primary election that featured Barry Goldwater and Nelson Rockefeller. Debate within the Republican Party led Buckley to state his support for "the rightwardmost viable candidate." It is often misquoted and misapplied as proclaiming support for "the rightwardmost electable candidate" or simply the most electable candidate.

In 1965, Buckley ran for mayor of New York City as the candidate for the new Conservative Party. He ran to restore momentum to the conservative cause in the wake of Goldwater's defeat. He tried to take votes away from the relatively liberal Republican candidate and fellow Yale alumnus John Lindsay, who later became a Democrat. Buckley did not expect to win; indeed, when asked what he would do if he won the race, Buckley responded, "Demand a recount." and used an unusual campaign style; during one televised debate with Lindsay, Buckley declined to use his allotted rebuttal time and instead replied, "I am satisfied to sit back and contemplate my own former eloquence."

For many Americans, Buckley's erudition on his weekly PBS show Firing Line (1966–1999) was their primary exposure to him and his use of erudite, multisyllabic vocabulary which was Common in academia but unusual on television.

When asked if there was one person with whom Buckley would not share a stage, Buckley's response was Gore Vidal. Likewise, Vidal's antagonism toward Buckley was well known, even before 1968. Buckley appeared in a series of televised debates with Vidal during the 1968 Republican National Convention in Miami and the Democratic National Convention in Chicago.

This feud continued the following year in the pages of Esquire, which commissioned essays from both Buckley and Vidal on the television incident. Buckley's essay "On Experiencing Gore Vidal" was published in the August 1969 issue. In September, Vidal responded with his own essay, "A Distasteful Encounter with william F. Buckley." In it Vidal strongly implied that, in 1944, Buckley's unnamed siblings, and possibly Buckley himself, had vandalized a Protestant church in their Sharon, Connecticut, hometown after the pastor's wife had sold a house to a Jewish family. He also implied that Buckley was a homosexual and a "racist, antiblack, anti-Semitic and a pro-crypto Nazi." Buckley sued Vidal and Esquire for libel; Vidal counter-claimed for libel against Buckley, citing Buckley's characterization of Vidal's novel Myra Breckenridge as pornography. After Buckley received an out-of-court settlement from Esquire, he also dropped the suit against Vidal. Both cases were dropped, with Buckley settling for court costs paid by Esquire Magazine, which had published the piece, while Vidal, who did not sue the magazine, absorbed his own court costs, but neither had paid each other compensation. Buckley also received an editorial apology in the pages of Esquire as part of the settlement.

In July of 1971, Buckley assembled a group of conservatives to discuss some of Nixon's domestic and foreign policies that the group opposed. In August of 1969, Nixon had proposed and later attemped to enact welfare legislation known as the Family Assistance Plan (FAP), which would establish a national income floor of $1600 per year for a family of four. On the international front he negotiated arms talks with the Soviet Union and initiated relations with China, which Buckley, as a hawk and anti-communist, opposed. The group, known as the Manhattan Twelve, included National Review’s publisher william A. Rusher and editors James Burnham and Frank Meyer. Other organizations represented were the newspaper Human Events, The Conservative Book Club, Young Americans for Freedom, and the American Conservative Union. On July 28, 1971, they published a letter announcing that they would no longer support Nixon. The letter said, “In consideration of his record, the undersigned, who have heretofore generally supported the Nixon Administration, have resolved to suspend our support of the Administration.” Buckley would later go on to join the adminisration as a delegate to the UN.

Epstein (1972) argues that liberals were especially fascinated by Buckley, and often wanted to debate him, in part because his ideas resembled their own, for Buckley typically formulated his arguments in reaction to left-liberal opinion, rather than being founded on conservative principles that were alien to the liberals.

In 1973, the Nixon Administration appointed Buckley to serve as a delegate to the United Nations, upon which Buckley would later write a book. In 1981, Buckley informed President-elect (and personal friend) Ronald Reagan that he would decline any official position offered to him. Reagan jokingly replied that was too bad, because he had wanted to make Buckley ambassador to (then Soviet-occupied) Afghanistan. Buckley replied that he was willing to take the job but only if he were to be supplied with "10 divisions of bodyguards".

In 1975, Buckley recounted being inspired to write a spy novel by Frederick Forsyth's The Day of the Jackal: "...If I were to write a book of fiction, I'd like to have a whack at something of that nature." He went on to explain that he was determined to avoid the moral ambiguity of Graham Greene and John le Carré. Buckley wrote the 1976 spy novel Saving the Queen, featuring Blackford Oakes as a rule-bound CIA agent, based in part on his own CIA experiences. Over the next 30 years, he would write another ten novels featuring Oakes. New York Times critic Charlie Rubin wrote that the series "at its best, evokes John O'Hara in its precise sense of place amid simmering class hierarchies". Stained Glass, second in the series, won a 1980 National Book Award in the one-year category Mystery (paperback).

Buckley began writing on computers in 1982, starting with a Zenith Z-89. According to his son, Buckley developed an almost fanatical loyalty to WordStar, installing it on every new PC he got despite its growing obsolescence over the years. Buckley used it to write his last novel, and when asked why he continued using something so outdated, he answered "They say there's better software, but they also say there's better alphabets."

In an op-ed piece in The New York Times on March 18, 1986, Buckley addressed the AIDS epidemic. Calling it "a fact" that AIDS is "the special curse of the homosexual," Buckley argued that people infected with the disease could only marry if they agreed to sterilization and that universal testing—led by insurance companies, not the government—should be mandatory. Most controversially of all, he wrote: "Everyone detected with AIDS should be tattooed in the upper forearm, to protect common-needle users, and on the buttocks, to prevent the victimization of other homosexuals." The piece led to much criticism; some gay Activists advocated boycotting Patricia Buckley's fund-raising efforts for AIDS. william Buckley later back-tracked from the piece, but in 2004 he told The New York Times Magazine, "If the protocol had been accepted, many who caught the infection unguardedly would be alive. Probably over a million."

In 1988, Buckley helped defeat liberal Republican Senator Lowell Weicker in Connecticut. Buckley organized a committee to campaign against Weicker and endorsed his Democratic opponent, Connecticut Attorney General Joseph Lieberman.

In 1991, Buckley received the Presidential Medal of Freedom from President George H. W. Bush. Upon turning 65 in 1990, he retired from the day-to-day running of the National Review and relinquished his controlling shares of National Review in June 2004 to a pre-selected board of trustees. The following month he published the memoir Miles Gone By. Buckley continued to write his syndicated newspaper column, as well as opinion pieces for National Review magazine and National Review Online. He remained the ultimate source of authority at the magazine and also conducted lectures, and gave interviews.

Appel (1992) argues from rhetorical theory that Buckley's essays are often written in "low" burlesque in the manner of Samuel Butler's satirical poem "Hudibras". Considered as drama, such discourse features black-and-white disorder, a guilt-mongering logician, distorted clownish opponents, limited scapegoating, and a self-serving redemption.

In his 1997 book Nearer, My God, he condemned what he viewed as "the Supreme Court's war against religion in the public school", and argued that Christian faith was being replaced by "another God ... multiculturalism". As an adult, Buckley regularly attended the traditional Latin Mass in Connecticut. He disapproved of the liturgical reforms following the Second Vatican Council. Buckley also revealed an interest in the writings and revelations of the 20th Century Italian Writer Maria Valtorta. In his spiritual memoir, Buckley reproduced Valtorta's detailed accounts of Jesus Christ's crucifixion, which were based on Valtorta's visionary experiences of Christ and the mystical revelations she reported experiencing between the years 1943–47, being shown Jesus' life in 1st-century Israel and recording the visions in her book The Poem of the Man-God.

Regarding Donald Trump, he described him in 2000 as a "demagogue" and a "narcissist."

The feud was reopened in 2003 when Esquire republished the original Vidal essay, at which time further legal action against the magazine resulted in Buckley's being compensated both personally and for his legal fees, along with an editorial notice and apology in the pages of Esquire, again.

About neoconservatives, he said in 2004: "I think those I know, which is most of them, are bright, informed and idealistic, but that they simply overrate the reach of U.S. power and influence."

In 1951, along with many other Ivy League alumni, Buckley was recruited into the Central Intelligence Agency (CIA); he served for two years including one year in Mexico City working on political action for E. Howard Hunt, who was later jailed for his part in The Watergate affair. The two officers remained lifelong friends. In a November 1, 2005, column for National Review, Buckley recounted that while he worked for the CIA, the only employee of the organization that he knew was Hunt, his immediate boss. While in Mexico, Buckley edited The Road to Yenan, a book by Peruvian author Eudocio Ravines.

Regarding the War in Iraq, Buckley stated, "The reality of the situation is that missions abroad to effect regime change in countries without a bill of rights or democratic tradition are terribly arduous." He added: "This isn't to say that the Iraq war is wrong, or that history will judge it to be wrong. But it is absolutely to say that conservatism implies a certain submission to reality; and this war has an unrealistic frank and is being conscripted by events." In a February 2006 column published at National Review Online and distributed by Universal Press Syndicate, Buckley stated unequivocally that, "One cannot doubt that the American objective in Iraq has failed." Buckley has also stated that "...it's important that we acknowledge in the inner councils of state that it (the war) has failed, so that we should look for opportunities to cope with that failure."

Buckley was an advocate for the legalization of marijuana and some drug legalization as early as his 1965 candidacy for mayor of New York City. He wrote a pointed pro-marijuana legalization piece for National Review in 2004 where he calls for conservatives to change their views on legalization, stating, "We're not going to find someone running for President who advocates reform of those laws. What is required is a genuine republican groundswell. It is happening, but ever so gradually. Two of every five Americans [...] believe 'the government should treat marijuana more or less the same way it treats alcohol: It should regulate it, control it, tax it, and make it illegal only for children.'" In his December 3, 2007 column, shortly after his wife's death, which he attributed, at least in part, to her smoking, Buckley seemed to advocate banning tobacco use in America.

Lee (2008) argues that Buckley introduced a new rhetorical style that conservatives often tried to emulate. The "gladiatorial style", as Lee calls it, is flashy and combative, filled with sound bites, and leads to an inflammatory drama. As conservatives encountered Buckley's arguments about government, liberalism and markets, the theatrical appeal of Buckley's gladiatorial style inspired conservative imitators, becoming one of the principal templates for conservative rhetoric.

In their penultimate debate on August 28 of that year, the two disagreed over the actions of the Chicago Police Department and the protesters at the ongoing convention. In reference to the response of the police involved in supposedly taking down a Viet Cong flag, moderator Howard K. Smith asked whether raising a Nazi flag during the Second World War would have elicited a similar response. Vidal responded that people were free to state their political views as they saw fit, whereupon Buckley interrupted and noted that people were free to speak their views but others were also free to ostracize them for holding those views, noting that in the U.S. during the Second World War "some people were pro-Nazi and they were well treated by those who ostracized them—and I'm for ostracizing people who egg on other people to shoot American Marines and American Soldiers. I know you [Vidal] don't care because you have no sense of identification with—". Vidal then interjected that "the only sort of pro- or crypto-Nazi I can think of is yourself," whereupon Smith interjected, "Now let's not call names." Buckley, visibly angered, rose several inches from his seat and replied, "Now Listen, you queer, stop calling me a crypto-Nazi or I'll sock you in your goddamn face, and you'll stay plastered." Buckley later apologized in print for having called Vidal a "queer" in a burst of anger rather than in a clinical context, but also reiterated his distaste for Vidal as an "evangelist for bisexuality": "The man who in his essays proclaims the normalcy of his affliction, and in his art the desirability of it, is not to be confused with the man who bears his sorrow quietly. The addict is to be pitied and even respected, not the pusher." The debates are chronicled in the 2015 documentary Best of Enemies.