Gillmor worked at the Kansas City Times and several newspapers in Vermont, followed by six years at the Detroit Free Press.

From 1994 to 2005, Gillmor was a columnist at the San Jose Mercury News, Silicon Valley’s daily newspaper, during which time he became a leading chronicler of the dot-com boom and its subsequent bust.

Starting in October 1999, he wrote a weblog for The Mercury News, which is believed to have been the first by a journalist for a traditional media company.

[4] Gillmor left The Mercury News in January 2005 to work on a start-up venture in citizen journalism called Bayosphere, which aimed to "make it easier for the public to report and publish on the Internet.

[8] In November 2007, Gillmor was named founding director of Arizona State University's new Knight Center for Digital Media Entrepreneurship at the Walter Cronkite School of Journalism and Mass Communication.