Wann attended Stanford University, earning a bachelor's degree in linguistics and a master's degree in modern thought and literature. As an undergraduate she wrote for the Stanford Daily. About five years after graduation she became an activist after being denied health insurance due to her weight. She began to speak out against weight prejudice and discrimination.
Her magazine Fat!So? was first released in summer of 1994. Her book Fat!So? Because You Don't Have to Apologize for Your Size was published in 1998. She writes about discrimination against fat people in health care, health insurance, and earning potential, and challenges the "anti-fat" mentality of many companies.[who?] She writes in her "Fat!so? Manifesto":
...being fat [is] like [...] being short or tall, or black or brown. These are facts of identity that cannot and should not be changed. They are birthright.
At 5'4" and about 300 pounds, she identifies as a fat person. She has served on the National Association to Advance Fat Acceptance (NAAFA) board; has swum with the Padded Lilies fat synchronized swim team; has performed with Big Moves modern ensemble and its hiphop troupe the Phat Fly Girls; and has done street actions with the Bod Squad fat pride cheerleaders. She is a supporter of Health At Every Size® (HAES) and explains that it is possible to be "fat and fit."
Wann has continued her activism with the creation of the Yay! Scale™ (which gives compliments instead of a number), speeches at multiple conferences and symposia, and continued involvement with the online 'fatosphere' of fat activist bloggers. She has appeared on national media such as ABC,CBS, and CNN.
In 2007, Wann interviewed Leonard Nimoy of Star Trek fame, about his work in photography of nude fat models. She participated in a lecture series given at the University of Oklahoma on "Food, Culture & Society" in November 2007. In addition to her scheduled lecture, Marilyn Wann took time to teach students how to make Yay Scales to celebrate weight diversity.
Marilyn Wann is well known for condoning the weight of others, and essentially encouraging them to not loose weight. She even goes so far as to tell the readers of her column that being over weight "is not a death sentence", all the while disregarding the massive amounts of data that indicate being over weight is extremely unhealthy. 
- Fat-pride instigator is battling against weight discrimination, Deseret News, February 20, 2006
- Book review, Newsday, April 6, 1999
- Living Large: Marilyn Wann is fat. Got a problem with that?, Stanford Alumni Magazine, July–August 2003
- Fat! Fit? Fabulous, East Bay Express, September 13, 2006
- Fat Lash, ABC, October 19, 2004
- Flap over "Fat Fliers", CBS News, May 27, 2009
- Size discrimination laws: Weighing pros, cons, Crossfire, CNN, May 9, 2002
- Full On with Leonard Nimoy, Smith MagazineDecember 1, 2007
- Weight Loss: Health Risks Associated with obesity