Dowd was born the youngest of five children in Washington, D.C. Her mother, Margaret "Peggy" (Meenehan), was a housewife, and her father, Mike Dowd, worked as a Washington, D.C. police inspector. Dowd graduated from (now defunct) Immaculata High School in 1969. She received a B.A. in English in 1973 from The Catholic University of America in Washington, D.C.

During the 1970s and the early 1980s, Dowd worked for Time magazine and the Washington Star, where she covered news and Sports and wrote feature articles. Dowd joined The New York Times in 1983 as a Metropolitan Reporter, and became an op-ed Writer for the newspaper in 1995. In 1999, Dowd was awarded a Pulitzer Prize for her series of columns on the Monica Lewinsky scandal in the Clinton administration.

Dowd began her career in 1974 as an editorial assistant for the Washington Star, where she later became a Sports columnist, metropolitan reporter, and feature Writer. When the newspaper closed in 1981, she went to work at Time. In 1983, she joined The New York Times, initially as a metropolitan reporter. She began serving as correspondent in the Times Washington bureau in 1986.

In 1991, Dowd received a Breakthrough Award from Columbia University. In 1992, she was a Pulitzer Prize finalist for national reporting, and in 1994 she won a Matrix Award from New York Women in Communications.

Dowd became a columnist on The New York Times op-ed page in 1995, replacing Anna Quindlen, who left to become a full-time Novelist. Dowd was named a Woman of the Year by Glamour magazine in 1996, and won the 1999 Pulitzer Prize, for distinguished commentary. She won The Damon Runyon Award for outstanding contributions to journalism in 2000, and became the first Mary Alice Davis Lectureship speaker (sponsored by the School of Journalism and the Center for American History) at The University of Texas at Austin in 2005. In 2010, Dowd was ranked #43 on The Daily Telegraph's list of the 100 most influential liberals in America; in 2007, she was ranked #37 on the same list.

Dowd's columns have also been described as often being political cartoons that capture a caricatured view of the current political landscape with precision and exaggeration. For Example, in the run-up to the 2000 presidential election Dowd wrote that Democratic candidate "Al Gore is so feminized and Diversified and ecologically correct that he's practically lactating," while referring to the Democratic party as the "mommy party". In a Fresh Dialogues interview years later she said, "I was just teasing him a little bit because he was so earnest and he could be a little righteous and self important. That’s not always the most effective way to communicate your ideas, even if the ideas themselves are right. I mean, certainly his ideas were right but he himself was – sometimes – a pompous messenger for them."

On March 4, 2014, Dowd published a column about the dominance of men in the film industry; in it, she quoted Amy Pascal, co-chairman of Sony Pictures Entertainment. According to BuzzFeed, "leaked emails from Sony" suggested that Dowd had promised to provide the draft column to Pascal's husband, former Times reporter Bernard Weinraub, prior to the column's publication. BuzzFeed said the column "painted Pascal in such a good light that she engaged in a round of mutual adulation with Dowd over email after its publication." Both Dowd and Weinraub have denied that Weinraub ever received the column. On December 12, 2014, Times public Editor Margaret Sullivan concluded, "While the tone of the email exchanges is undeniably gushy, I don’t think Ms. Dowd did anything unethical here." In August 2014, it was announced that Dowd would become a staff Writer for The New York Times Magazine. Her first article under the new arrangement was published more than a year later.

On May 2, 2015, Dowd published a column in the Times about her niece Tara, who had a stroke at age 41 caused by an arterial dissection in her brain. Prior to the stroke, Tara had been a very active athlete. The first Neurologist who saw Tara told her to cut back on physical activity, but a second Neurologist, Dr. Louis R. Caplan, a Harvard Neurologist, disagreed with the first Neurologist and said that they had misinterpreted the images of her brain and vascular system. He told her to return to exercise, which she did safely. In the article, Dr. Caplan suggested that going to the emergency rooms was "dangerous" and compared ERs to "local gas stations" where you should not get your brain, a "Rolls-Royce," serviced. He suggested that one should be 'pushy' and since E.R. people have to deal with a lot of organs quickly, and they get little neurology training, you should ask for a Neurologist. He said that stroke experts "have had a hard time getting the message across to E.R. personnel that if a stroke is suspected, a vascular image must be taken as well as a brain image, because it shows up first in the vessels that supply and drain the brain". Ultimately he recommended that you should "find an academic medical center that has a specialization in stroke". These comments unleashed a firestorm of comments from emergency Medicine Physicians on social media, who thought that Caplan's comments were poorly informed and reckless, particularly sending the message not to go to the ER for symptoms of stroke, which directly contradicts recommendations from the American Heart Association to "call 9-1-1" when experiencing signs of stroke. In a related column in The Huffington Post, Dr. David Newman, an ER physician from Mount Sinai, wrote that Dr. Caplan's comments showed "poor insight" and "narrow expertise", claiming that subspecialty Medicine as a whole was expensive and often unnecessarily invasive.