Chretien grew up on a horse farm in Gray and New Gloucester, Maine with his mother, Eileen, his father, Mike, and his younger brother, Joel. After graduating from Gray-New Gloucester High School, he entered Middlebury College in 1988, but after a year, left to spend eight months teaching English in El Salvador and Nicaragua. He returned to school in 1991, entering Columbia University. He left Columbia before graduating, after having been suspended for a semester for involvement in the protest occupation of a campus building. In 1994 he moved to the San Francisco Bay Area, where he graduated from San Francisco State University in 2003 with a B.A. in history. Chretien lives in Oakland, California, with his wife, Jessie Muldoon, an Oakland public school teacher, and their daughter Isabela.