Born in Aalborg, Denmark to a Danish mother and American father, Bumiller moved to the U.S. when she was three years old. She moved to Cincinnati, where she graduated from Walnut Hills High School in 1974. She is a 1977 graduate of Northwestern University.

She has been married since 1983 to Steven R. Weisman, also a former White House correspondent, who reported from India and Japan for the New York Times and is now editorial director and public policy fellow at the Peterson Institute for International Economics. The couple have two children.

Bumiller was the Times' White House correspondent from September 10, 2001 until 2007. She has been criticized, along with other White House reporters, for not questioning George W. Bush aggressively during a press conference in the run-up to the Iraq war. Bumiller said, on the press conference in 2003 on the eve of the U.S. invasion of Iraq:

I think we were very deferential because ... it's live, it's very intense, it's frightening to stand up there. Think about it, you're standing up on prime-time live TV asking the president of the United States a question when the country's about to go to war. There was a very serious, somber tone that evening, and no one wanted to get into an argument with the president at this very serious time.

In 2003, in an article headlined "Keepers of Bush Image Lift Stagecraft to New Heights," she wrote of the president's famous "Mission Accomplished" speech, "George W. Bush's Top Gun landing on the deck of the carrier Abraham Lincoln will be remembered as one of the most audacious moments of presidential theater in American history," and described it as "the latest example of how the Bush administration [is] going far beyond the foundations in stagecraft set by the Reagan White House."

At a panel discussion sponsored by Northwestern's Medill School of Journalism on November 4, 2004, in Washington, D.C., Bumiller elicited audience laughter when she stated, "You can't just say the president is lying." Speaking about the challenges of presenting balanced news reporting, she had earlier said,

"That’s why it’s very hard to write those, because you can’t say George Bush is wrong here. There’s no way you can say that in the New York Times. So we contort ourselves up and say, “Actually”... I actually once wrote this sentence: “Mr. Bush’s statement did not exactly . . . ” It was some completely upside down statement that was basically saying he wasn’t telling the truth."

When the moderator asked shortly after why she couldn't "just say the president is lying," she responded,

"You can in an editorial, but I’m sorry, you can’t in a news column. Mr. Bush is lying?...You can say Mr. Bush’s statement was not factually accurate. You can’t say the president is lying...that’s a judgment call."

For her coverage of the 2004 presidential election, the New York Press crowned her the winner of the Worst Campaign Journalist award out of a field of 32 professional journalists. According to the Press article written by Matt Taibbi, her disregard for details and focus on process rather than policy questions were her main qualifications for the dishonor.

In 2008, Bumiller became involved in controversies related to her coverage of Senator John McCain's presidential campaign for the New York Times. In March 2008, she and McCain argued over questions she put to him regarding Senator John Kerry's proposal that McCain be his running mate. During the argument, Bumiller asked McCain "Can I ask you about your why you’re so angry?"

In September 2008, Bumiller wrote a front page article in the Times raising questions about the McCain campaign's vetting of vice presidential nominee Sarah Palin. Bumiller's article incorrectly reported that Palin had previously been a member of the Alaska Independence Party. After the McCain campaign criticized Bumiller's reporting, the Times corrected the inaccurate report.

She was chastised on June 6, 2009, by Times Public Editor Clark Hoyt for a front page article she wrote based on leaked Pentagon documnents which purported to show that about one in seven of the 534 prisoners transferred abroad from Guantánamo had “returned to terrorism or militant activity.” Hoyt wrote that the article was "seriously flawed and greatly overplayed". He added that it "demonstrated again the dangers when editors run with exclusive leaked material in politically charged circumstances and fail to push back skeptically." The lapse was especially unfortunate at The Times, Hoyt wrote, "given its history in covering the run-up to the Iraq war."

She is the author of May You Be the Mother of a Hundred Sons, a study of women's roles in 1980s Indian society, as well as The Secrets of Mariko, a book focusing on the inner workings of a Japanese family during a year in the early 1990s.

In 2007, Bumiller went on leave to write a biography of U.S. Secretary of State Condoleezza Rice, published by Random House in December 2007. War Room — Salon.com The book portrays Rice catering to Bush's desire to invade Iraq, and it describes her being taken completely by surprise when Hamas won the Palestinian elections.She returned to the paper full time in October 2007.