From 2003 to 2008, he served as an assistant United States attorney in the District of Wyoming.

[3] On June 7, 2012, he assumed office as a United States magistrate judge for the District of Wyoming.

[3] His nomination received support from Senators John Barrasso and Cynthia Lummis.

President Biden nominated Rankin to the seat vacated by Judge Nancy D. Freudenthal, who assumed senior status on June 1, 2022.

[9] On March 7, 2024, the United States Senate confirmed his nomination by voice vote.