Born in Huron, South Dakota, Viken earned a Bachelor of Arts from the University of South Dakota in May 1974 and a Juris Doctor from the University of South Dakota School of Law in May 1977.

From 1977 to 1981, Viken served as an assistant United States attorney for the District of South Dakota and in 1981 became the Acting United States Attorney for the District of South Dakota.

[2][1] In 2003, Viken was appointed the federal public defender for the District of South Dakota by the United States Court of Appeals for the Eighth Circuit.

[1] On June 25, 2009, President Barack Obama nominated Viken to a vacant seat on the United States District Court for the District of South Dakota that was created when Judge Lawrence L. Piersol assumed senior status.

[2] The United States Senate confirmed Viken on September 29, 2009 by a 99–0 vote.