After graduating from Ashby High School, Purdon graduated from North Dakota State College of Science in 1989 and from Minnesota State University Moorhead summa cum laude in 1991. He received his Juris Doctor from Hamline University School of Law in 1994.
Following his clerkship, Purdon practiced law at the firm of Dickson & Purdon in Bismarck, North Dakota. He then practiced law for the Vogel Law Firm, also in Bismarck, from 2005 to 2010. During this time, Minnesota Law & Politics Magazine named Purdon a "Great Plains Super Lawyer" in the practice area of Criminal Defense in 2007 and 2009.