He previously served as state secretary in the Ministry of Local Government and Regional Development from 2013, and represented Troms in the Norwegian parliament from 2005 until 2013.

[3] After the 2013 parliamentary election, Amundsen, located 2nd on the party list, lost his seat due to re-districting of Troms county.

[6] He resigned as chair in March 2024 following controversial comments made on Facebook regarding the Israel-Palestine conflict and women's rights.

[7] Helge André Njåstad succeeded him on 14 March, while Amundsen was moved to the Standing Committee on Local Government and Public Administration.

[8] On 20 December 2016, in a cabinet reshuffle, Amundsen was appointed Minister of Justice, succeeding fellow Progress Party politician Anders Anundsen.

[2] He was one of the Norwegian politicians together with Christian Tybring-Gjedde to propose Donald Trump as a candidate for Nobel Peace Prize.

[13] He has also sought to remove the public economical support for the Islamic Council Norway as it did not distance itself from the use of death penalty for homosexuality.

[18] In early 2019 Amundsen sparked a huge debate in Norway when he suggested for child support for non-western immigrants to be cut to stop them from "producing more children" and halt a possible decline of "ethnic Norwegians" in the population.

Some commentators denounced Amundsen intentions and tone of speech as racist and out of line with the principles of Norwegian politics and community.

[21] Amundsen supports oil exploration off the Lofoten archipelago, a major breeding ground for Atlantic cod.

[23] Amundsen wants Norway to give asylum to UK right wing activist Tommy Robinson, who was given a nine-month jail sentence in 2019.

[24] In March 2024, Amundsen caused controversy when he responded to Facebook comments accusing Israel supporters of genocide.

The Green Party's Une Bastholm called for Storting President Masud Gharahkhani to consider removing Amundsen as chair of the Standing Committee on Justice.