Armstrong was born Heather Hamilton in 1975 and raised in Memphis, Tennessee. Raised in the LDS Church, she began having doubts about it and experiencing bouts of depression while a student at Brigham Young University (BYU) in predominantly Mormon Utah. After graduating in 1997, she left both the church and state, relocating to Los Angeles where she found work as a web developer for startups during the dot-com boom.

Armstrong says the following about her site, dooce.com, which began in February 2001 with a post about Carnation Milk: “Since then I have published more than 5,300 entries covering topics such as breast milk pumps, golf cart rides with Norah Jones, and the one guy I dated who talked like Elmo during sex.”

In 2002, Armstrong ignited a fierce debate about privacy issues when she was allegedly fired from her job as a web designer and graphic artist because she had written satirical accounts of her experiences at a dot-com startup on her personal blog, dooce.com. She did not challenge her termination and has refrained from identifying her place of employment in interviews.

Armstrong kept blogging in the wake of her termination, and through a mutual friend met Jon Armstrong, another former Mormon web developer from Utah. They married and returned to their home state to start a family. In 2004, after the couple’s first daughter was born, Armstrong began devoting much of her blog to parenting, becoming one of the first mommybloggers.

In 2004, Armstrong accepted text advertisements on her website for the first time, a decision that was controversial among her readership. The following year, Armstrong accepted graphic ads and wrote that the revenue from the advertisements would be her family’s principal source of income while her husband made the transition to manage her advertising and business. Since then, she has appeared in Suave advertisements that feature her own image and trademark. In 2009, Armstrong again received mass media attention for using Twitter to get her washing machine fixed.

In late 2005, Armstrong entered into negotiations with Kensington Books to produce two books, one of which was to be a memoir of early parenthood. The negotiations broke down in May 2006, and Kensington sued to force Armstrong to fulfill the terms of the unsigned contract. In October 2006 both parties agreed to a settlement which allowed Armstrong to seek another publisher.

Dooce.com has received multiple nominations and awards from The Weblog Awards, including a lifetime achievement award for Armstrong in 2008.

Kensington Books released a book of essays, Things I Learned About My Dad: In Therapy, on April 29, 2008, edited by Heather B. Armstrong.

“Dooced” can mean “getting fired for something you’ve written on your website”, a sense humorously disavowed by Armstrong in her blog’s FAQ. This definition was used by the television game show Jeopardy! on December 10, 2009, as evidenced by a screenshot on her blog the following day.

Her second book, It Sucked and Then I Cried: How I Had a Baby, a Breakdown, and a Much Needed Margarita was released on March 24, 2009 and published by Simon Spotlight Entertainment. It reached #16 on The New York Times Bestseller List for April 12, 2009.

In late 2009, Armstrong announced a partnership with the television network HGTV in which she would “work with HGTV’s online and on-air production teams to create innovative convergence programming for the network.” While the bulk of her partnership activities began in the spring of 2010, Armstrong began contributing weekly content to the network’s Design Happens blog in February 2010. Her last post on Design Happens was in September 2010.

Dooce also attracted attention from websites devoted to making sardonic and critical observations about lifestyle bloggers, such as Get Off My Internets and the subreddit blogsnark. The mostly female readers of those forums second-guessed Armstrong’s parenting decisions and suggested she did not appreciate how privileged she was. Heather responded by posting hate mail she received from the readers of those sites on a separate page, which she has since taken down, called “Monetizing the Hate”; Jon joked in 2011 that the traffic from the hate sites had been better for the family business than the birth of their second daughter two years earlier. By then the revenue from Dooce paid salaries not only to the Armstrongs but an assistant and two full-time babysitters.

The Armstrongs announced they were separating in 2012; Heather posted to Dooce explaining why while Jon posted on his blog, Blurbomat. At the time the announcement came as a surprise since Heather had never written about any marital difficulties, and had often written positively of her husband’s support for her during her struggles with the children and her depression. Later, she said the couple had at that point been in counseling for years; Jon was “controlling and punishing” and expected her to just get over the negative commentary on her site.

In 2015, Armstrong announced that she would be taking a step back from blogging in order to focus on speaking and consulting work. While she was able at first to travel and make speaking engagements, and do some freelance marketing work, she soon found the pressures of single parenthood overwhelmed her. Depression returned and by 2017, Armstrong says she felt like “a heap of nothingness” and could not go on living.

Armstrong returned to a different Internet. Most lifestyle bloggers like her had been replaced by, or evolved into, influencers. “Mommy blogging is dead, and I think most of my colleagues would agree”, she told Vox in 2019.