Hamsher is a Massachusetts native who lived in Fitchburg and then Attleboro. Her family moved to Seattle when she was eight years old. She attended Roosevelt High School. She went on to attend Mills College in Oakland, California, and studied abroad in London. In college Hamsher worked as a reporter covering punk rock and politics for the San Francisco Bay Guardian. She also edited Damage, a punk rock fanzine. After college she moved to Los Angeles, where she was accepted into the Peter Stark Producing Program at the USC School of Cinema-Television. She received her M.F.A. in 1988.

In September 1997, Hamsher published the controversial memoir Killer Instinct recounting her experiences as a producer of Natural Born Killers. The L.A. Times said the book is “chock-full of outrageous firsthand tales.” As Entertainment Weekly put it, “Stone is painted as a hard-partying womanizer who pits his underlings against each other and plays mind games….Tarantino gets off less easily. Hamsher charges that he betrayed her and Murphy by going behind their backs to keep them from making Natural Born Killers. She also calls Tarantino a ‘one-trick pony,’ a wildly overrated director.” Hamsher included a full-page reproduction of a suggestive note Tarantino allegedly sent her at the Venice Film Festival. On his website, Murphy says that when Tarantino’s former manager, Cathryn Jaymes, “came back with her notes [on the manuscript] my then partner lost it on her, I guess because she didn’t want to make changes. There are many reasons why our partnership ended soon after that book, but her treatment of Cathryn was a major factor.” Killer Instinct reached number two on the L.A. Times bestseller list. Hamsher was later sued by an attorney who is described in the book as a “creepazoid attorney,” “the Kmart Johnnie Cochran” and “a loser wannabe lawyer.” The Appeals Court affirmed that colorful language which does not impugn professional abilities is protected by the First Amendment.”

Hamsher lived in the Los Angeles area for most of her career as a producer. She sold her Nichols Canyon house in 2004 and moved to Otter Rock, Oregon. When she became interested in the 2006 Connecticut Senate race, she rented a small farmhouse in Guilford, Connecticut, where she and other bloggers and reporters could live while covering the campaign. A few months later she raised money for a similar rental in Washington, D.C., called “Plame House”, which served as a base for covering the Scooter Libby trial. She now has a residence in Washington, D.C.

On April 7, 2008, she was a guest speaker in the panel discussion entitled “Intelligentsia” co-hosted by Elle and OfficeMax, along with Publisher of Elle Magazine Carol Smith, actress Melora Hardin, Vice President of Marketing for OfficeMax Julie Krueger, Editor in Chief of Elle Magazine Roberta Myers, footwear designer Taryn Rose, and Creative Director of Barneys Simon Dunan, at the Plaza Hotel, in New York City.

Among other blogger conference programs, she participated in the South by Southwest (SXSW) Interactive Panels, held in Austin, Texas, from March 9 to 13, 2007, in which she also moderated Dan Rather’s “Keynote Interview” event on Monday, March 12, and in the panel on “Political Blogging: Macaca Mania” at the BlogWorld & New Media Expo 2008, in Las Vegas, Nevada, on September 20, 2008.

Hamsher took her mother’s maiden name. Her family name is Murphy. In 2009, Hamsher told Politico that she dated then-SEIU President Andy Stern for two years. She lives with her poodles Katie and Lucy. When Kobe, her third, died in 2009 she wrote a 5,000-word tribute.

Jane Hamsher is listed as leading the CommonSense Media Advertising Network, which includes Eschaton, FireDogLake, FiveThirtyEight, and Think Progress. The company filed for Chapter 7 Bankruptcy in the District of Columbia Bankruptcy Court on March 3, 2013