While Moore was briefly a student at University of Michigan-Flint, he dropped out to focus on activism, and began a career as a journalist by working for the Flint Voice, an alternative weekly newspaper. In time, Moore became the editor, and under his leadership the paper expanded into the Michigan Voice, one of the most respected alternative political publications in the Midwest. Moore's success at the Michigan Voice eventually led to a job offer from Mother Jones magazine, where he became editor in 1986. Moore believed that Mother Jones, a leftist political journal based in San Francisco, had lost its bite, and it was his goal to give the magazine an edgy, populist voice. He often butted heads, however, with Mother Jones' publishers and management, and after less than a year he was fired, reportedly for refusing to run an article critical of the Sandanista rebels in Nicaragua that Moore believed was both inflammatory and inaccurate.

After a brief spell working with a Ralph Nader organization, Moore got the idea to make a film about his old hometown of Flint and how the local economy had collapsed in the wake of the closure of General Motors' Flint plants despite their continued profitability. Moore used his settlement fee from Mother Jones as seed money for the film, but eventually sold his home and even held bingo games to raise the money to finish it. Finally, in 1989, the completed film Roger & Me -- in which, among other things, Moore and his crew repeatedly fail to get General Motors chairman Roger Smith to agree to an interview -- became a major critical success, was honored at a number of film festivals, and went on to become one of the most financially successful documentary features ever made.

Following the success of Roger & Me, Moore participated as an interviewer in the production of Blood in the Face, a documentary about extremist White Power groups (co-directed by Roger & Me's cameraman, Kevin Rafferty), and then directed a short follow-up to Roger & Me, Pets or Meat: The Return to Flint, which followed what had happened there since the previous film's conclusion. Next, Moore began work on his first fictional feature, Canadian Bacon, a satiric comedy in which an ineffectual United States president fabricates a "Cold War" against Canada. Unfortunately, John Candy, who played the lead, died shortly after filming was wrapped, which, in part, led to conflicts with the film's producers that prevented it from receiving a wide release. In 1994, Moore took his first stab at television with the satiric news and commentary program TV Nation, which aired on NBC. While TV Nation won rave reviews and a loyal following, the show's ratings were not what NBC was hoping for (it was also uncomfortable with some of the show's satire), and the network canceled the show after only one season. FOX stepped forward to air a second season of TV Nation, but the show fared no better on FOX and soon went off the air for good.

In 1996, Moore returned to the written word, publishing a book of political commentary, Downsize This!: Random Threats From an Unarmed American. The book proved to be a surprise best-seller, and as Moore took to the road to promote it, he brought a camera crew along to make a documentary exploring the economic inequality in America as he dashed from city to city; the resultant film, The Big One, was released in 1998. In 1999, Moore returned to television with The Awful Truth, a blend of comedy and pointed political commentary similar to TV Nation. Rather than deal with U.S. network interference again, Moore got financial backing from the British network Channel Four, with the cable outlet Bravo airing the show in the United States; the show lasted two seasons.

In the fall of 2001, Moore's next book, Stupid White Men, was scheduled for publication when its release was postponed by its publisher, Random House; Moore was openly critical of George W. Bush in the book, and after the terrorist attacks of September 11, 2001, Random House felt that the book's satiric tone would be considered inappropriate. According to Moore, Random House was considering canceling the book and destroying its initial print run (which was completed prior to 9/11) when he was asked about the book at a convention of library administrators. After telling the audience that the book was in all likelihood never coming out, an e-mail campaign was launched by librarians, and in the spring of 2002, Stupid White Men was finally released, quickly becoming a major best-seller.

In the fall of 2002, Moore released his fourth feature film, Bowling for Columbine, an examination of America's obsession with guns and violence. It was the first documentary to be shown in competition at the Cannes Film Festival in 46 years, and was honored with the festival's Jury Award. Subsequently becoming the most financially successful documentary in the history of film, Bowling for Columbine recieved a Best Documentary nomination when the 2002 Academy Award nominees were announced in February of 2003. The film subsequently won the Oscar, and true to form, Moore used his acceptance speech as an opportunity to launch a broadside against President George W. Bush and his participation in the war against Iraq, which had been launched only a few days before. Moore's statement drew strong reaction on both sides of the political fence, though Moore himself appeared to take the controversey in stride. In fact, the speech would prove to be only the tip of the iceberg as far as Moore's indictment of the Bush administration.

A little over a year after taking home his Academy Award, Moore accomplished the seemingly impossible task of topping Bowling for Columbine with his fifth feature, Fahrenheit 9/11. A scathing indictment of the Bush Administration that sought to expose financial ties between the Bush family and the relatives of terrorist Osama bin Laden, the film had its first success at the 2004 Cannes Film Festival where it was given both a twenty-minute standing ovation and the Palm D'or, making it the first documentary to ever win the festival's top prize. Despite the honor bestowed upon the film, it was nearly kept out of theaters when Disney chose not to allow Miramax to distribute it. Luckily, Miramax heads Bob and Harvey Weinstein were allowed to purchase the film back from Disney and a distribution deal was made with IFC and Lion's Gate. In June 2004, amid intense controversy, Fahrenheit 9/11 was released in just shy of 900 theaters and made nearly $22 million in its first weekend, breaking the total box-office record for a documentary previously held by Bowling for Columbine in just three days and becoming the first documentary ever to be crowned the top money-maker of the weekend.