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. During the 2008 Democratic presidential primary, Purdon served as North Dakota state chairman for the John Edwards campaign. In 2010, Purdon was nominated by President Barack Obama to be the United States Attorney for the District of North Dakota. He was unanimously confirmed by the United States Senate on August 5, 2010. As U.S. Attorney, Purdon gave special focus to making North Dakota's American Indian reservations safer for their residents and to countering the burgeoning organized crime activity that came with the increased oil activity in western North Dakota during his tenure. In 2013, Attorney GeneralEric Holder appointed Purdon the Chair of the Attorney General's Native American Issues Subcommittee, which is responsible for recommending policy to address issues that specifically impact American Indian communities. In this role, Purdon also represented the Department of Justice in testimony before the United States Senate Committee on Indian Affairs. In 2014, Holder appointed Purdon to the select Attorney General's Advisory Committee, which represents all U.S. Attorneys in advising the Department of Justice on criminal justice policy and department procedures. On February 10, 2015, Purdon announced he was stepping down from the position of U.S. Attorney, effective March 13, 2015. On his departure from the Justice Department, Attorney General Holder praised his tenure as U.S. Attorney for North Dakota stating that, "Tim Purdon has been an outstanding United States Attorney, a fierce advocate for the people of North Dakota and a strong national leader whose efforts to improve public safety in Indian Country have made a profound difference – and touched countless lives." Purdon then became a partner at Robins Kaplan LLP, for which he founded and opened a Bismarck office. In the summer of 2015, Purdon and former US Attorney for South Dakota Brendan Johnson founded Robins Kaplan's American Indian Law and Policy Group. Purdon co-chairs this group and the Government and Internal Investigations Group at Robins Kaplan.
