Smith was born in Villa Park, Orange County, California. In interviews, she has said she realized she wanted to be a writer sometime between kindergarten and first grade, “when a teacher praised a horrible poem I’d written”, and began writing in earnest in elementary school. Smith received a Bachelor of Arts degree in Experimental Psychology from the University of California at Santa Barbara in 1987, followed by teaching credentials in Elementary education and Special education from San Francisco State University.

She taught kindergarten and special education for several years before becoming a full-time writer. Her first book, The Night of the Solstice, was published by MacMillan in 1987, followed by, Heart of Valor in 1990, and the 4-volume Vampire Diaries series in 1991-2. Three trilogies followed: The Secret Circle (1992), The Forbidden Game (1994), and Dark Visions (1995). The first installment of her popular Night World series was published in 1996, followed by eight more over the next two years. In 1998, Smith began a decade-long hiatus from writing, returning in 2008 with a new Web site and a series of new short stories. The Vampire Diaries series was reissued in 2007, followed by re-printings of The Secret Circle trilogy and Night World series in 2008/2009. The Night of the Solstice and Heart of Valor was also reissued in 2008. Three new Vampire Diaries installments were published in 2009 and 2010.

Smith lives in the San Francisco Bay area “with one dog, three cats, and about ten thousand books.”