Gundersen served as the Chargé d'Affaires ad interim United States to Ukraine, Estonia, Iceland and Norway.

Gundersen served in numerous assignments both in the US and overseas, concentrating on the Nordic Region, arms control and political-military issues.

He served as Chargé d'Affaires and Deputy Chief of Mission in a number of nations, including Ukraine (1992), Estonia (1994-1995), Iceland and Norway.

He also teaches at the Joint Special Operations University and works for the State Department declassifying sensitive documents.

In the 2020 presidential election, Gundersen supported the Republican Voters Against Trump campaign for Democratic candidate Joe Biden.