He has been the leader of the Icelandic Independence Party since 2009, and served as the minister of finance and economic affairs from 2013 to 2017, a post he later retained under Katrín Jakobsdóttir and held until his resignation in October 2023.

[4] Bjarni entered the national parliament in 2003 and has been active in several committees in the areas of economy and taxation, industry and foreign affairs.

[7] On 17 May 2013 Icelandic media reported that Bjarni would take up the position of Minister of Finance and Economic Affairs in a cabinet led by Progressive Party leader Sigmundur Davíð Gunnlaugsson.

A new coalition between the Independence Party, Viðreisn and Bright Future was formed in January 2017 with Bjarni designated to become prime minister.

[11] Bjarni came under criticism in January 2017 for not revealing a government report on the offshore bank activities of Icelanders before the 2016 parliamentary elections.

[12] Shortly before midnight on 23 December 2020, police in Reykjavík dissolved a gathering of 40-50 people at the art gallery Ásmundarsalur for breach of COVID-19 restrictions.

Bright Future did this in the wake of reporting that government ministers of the Independence Party had concealed that Bjarni's father, Benedikt Sveinsson, recommended that the criminal record of convicted child sex offender Hjalti Sigurjón Hauksson be erased.

Bjarni resigned on 10 October 2023, following the release of a report by the Althing Ombudsman which heavily condemned his conduct relating to the sale of state-owned shares in the bank Íslandsbanki.

[24] In a meeting of Nordic foreign ministers in Oslo, Norway in November 2023, he refused to condemn Israel's bombing of the Jabalia refugee camp on the Gaza Strip the preceding day, questioning whether it could be described as an "attack” Bjarni stated: "It depends on what you define as an 'attack'".

[28] On 13 October, Bjarni announced that the government had collapsed due to disputes over foreign policy, asylum seekers, and energy, prompting him to call for new elections in November.