David Pasztor, managing editor of the Texas Observer, confirmed her death.
The writer, who made a living poking fun at Texas politicians, whether they were in her home base of Austin or the White House, revealed in early 2006 that she was being treated for breast cancer for the third time.
More than 400 newspapers subscribed to her nationally syndicated column, which combined strong liberal views and populist-toned humor. Ivins' illness did not seem to hurt her ability to deliver biting one-liners.
"I'm sorry to say (cancer) can kill you, but it doesn't make you a better person," she said in an interview with the San Antonio Express-News in September, the same month cancer claimed her friend, former Gov. Ann Richards.
To Ivins, "liberal" wasn't an insult term. "Even I felt sorry for Richard Nixon when he left; there's nothing you can do about being born liberal — fish gotta swim and hearts gotta bleed," she wrote in a column included in her 1998 collection, "You Got to Dance With Them What Brung You."
In a column in mid-January, Ivins urged readers to stand up against Mr. Bush's plan to send more troops to Iraq.
"We are the people who run this country. We are the deciders. And every single day, every single one of us needs to step outside and take some action to help stop this war," Ivins wrote in the Jan. 11 column. "We need people in the streets, banging pots and pans and demanding, 'Stop it, now!"'
Ivins' best-selling books included those she co-authored with Lou Dubose about Bush. One was titled "Shrub: The Short but Happy Political Life of George W. Bush" and another was "BUSHWHACKED: Life in George W. Bush's America."
Ivins' jolting satire was directed at people in positions of power. She maintained that aiming it at the powerless would be cruel.
"The trouble with blaming powerless people is that although it's not nearly as scary as blaming the powerful, it does miss the point," she wrote in a 1997 column. "Poor people do not shut down factories ... Poor people didn't decide to use 'contract employees' because they cost less and don't get any benefits."
In an Austin speech last year, former President Bill Clinton described Ivins as someone who was "good when she praised me and who was painfully good when she criticized me."
Ivins loved to write about politics and called the Texas Legislature, which she playfully referred to as "The Lege," the best free entertainment in Austin.
"Naturally, when it comes to voting, we in Texas are accustomed to discerning that fine hair's-breadth worth of difference that makes one hopeless dipstick slightly less awful than the other. But it does raise the question: Why bother?" she wrote in a 2002 column about a California political race.
Born Mary Tyler Ivins, the California native grew up in Houston. She graduated from Smith College in 1966 and attended Columbia University's journalism school. She also studied for a year at the Institute of Political Sciences in Paris.
Her first newspaper job was in the complaint department of the Houston Chronicle. She worked her way up at the Chronicle, then went on to the Minneapolis Tribune, becoming the first woman police reporter in the city.
Ivins counted as her highest honors that the Minneapolis police force named its mascot pig after her and that she was once banned from the campus of Texas A&M University, according to a biography on the Creators Syndicate Web site.
In the late 1960s, according to the syndicate, she was assigned to a beat called "Movements for Social Change" and wrote about "angry blacks, radical students, uppity women and a motley assortment of other misfits and troublemakers."
Ivins later became co-editor of The Texas Observer, a liberal Austin-based biweekly publication of politics and literature that was founded more than 50 years ago.
She joined The New York Times in 1976. She worked first as a political reporter in New York and later was named Rocky Mountain bureau chief, covering nine mountain states.
But Ivins' use of salty language and her habit of going barefoot in the office were too much for the Times, said longtime friend Ben Sargent, editorial cartoonist with the Austin American-Statesman.
"She's a force of nature," Sargent said.
Ivins returned to Texas as a columnist for the Dallas Times-Herald in 1982, and after it closed she spent nine years with the Fort Worth Star-Telegram. In 2001, she went independent and wrote her column for Creators Syndicate.
In 1995, conservative humorist Florence King accused Ivins in "American Enterprise" magazine of plagiarism for failing to properly credit King for several passages in a 1988 article in "Mother Jones." Ivins apologized, saying the omissions were unintentional and pointing out that she credited King elsewhere in the piece.
She was initially diagnosed with breast cancer in 1999, and had a recurrence in 2003. Her latest diagnosis came around Thanksgiving 2005.