Born in Hanford, California, Parnell is a graduate from the University of Puget Sound's School of Law (now known as Seattle University School of Law). He practiced law before being elected to the Alaska House of Representatives in 1992 and he continued to work in private legal practice while he was a member of the Alaska House and later, the Alaska Senate. He served two terms in the Alaska House from 1993 to 1997 before he was elected to one term in the Alaska Senate from 1997 to 2001. Parnell continued his legal career in the private sector, working as an attorney and as the state government relations director for Phillips Petroleum, now known as ConocoPhillips, and an attorney at the law firm Patton Boggs.