Founded in 1991 as the Washington Hemp Expo,[3][4] a self-described "humble gathering of stoners" attended by only 500 people,[4] and renamed the following year as Hempfest,[3] it has grown into a three-day annual political rally, concert, and arts and crafts fair[5] with attendance typically over 100,000.

Speakers have included Seattle city council member Nick Licata,[4] actor/activist Woody Harrelson (2004),[4] travel writer and TV host Rick Steves (2007), (2010),[4][6] 2012 Green Party speaker Jill Stein, Dallas Cowboys center Mark Stepnoski (2003),[4][7] and former chief of the Seattle Police Department Norm Stamper (2006).

About this time, the director was Dominic Holden, who was also campaign manager of an organization trying to make cannabis the city of Seattle's lowest law enforcement priority through a voter initiative, I-75.

[16] 2011 Hempfest speakers included numerous elected officials, among them Ohio congressman Dennis Kucinich, Seattle Mayor Mike McGinn, City Attorney Pete Holmes, a return by Councilman Licata, and Washington State Representatives Mary Lou Dickerson and Roger Goodman.

[17] 2013 saw the legalization of cannabis use in Washington state; that year's Seattle Hempfest featured performances by Everlast, Hed PE and DJ Muggs of Cypress Hill.