He was never elected a member of Parliament, but served nonetheless as Norwegian Minister of Foreign Affairs from 1935 to 1940, as part of the government-in-exile following Germany's invasion of Norway.

As an activist and politician he was described as a strong-willed and individualistic person, who nurtured a strong belief in taking an academic and legal perspective on political problems.

He was the second of four children born to Paul Steenstrup Koht (1844–1892), an educator and politician, and Betty Giæver (1845–1936), a part-time teacher with a penchant for singing, languages and drawing.

The family moved to Skien when Halvdan was twelve years old, where his father again immersed himself in politics: he served as mayor as well as parliamentarian for the Liberal Party.

[1] In September 1898 in Kristiania, Koht married Karen Elisabeth Grude (1871–1960), an essay writer and women's rights activist one and a half years his senior; they had three children.

[21] Ludvig Ludvigsen Daae exclaimed that a person whom Koht wanted to study, the farmer-politician John G. Neergaard, was a "crook ... oh well, trahit sua quemque voluptas".

Koht argued that the peasant movement had abandoned the cause of class interest in favour of universal rights and social reforms.

[1] An economic background for the farmers' rising was presented in 1912, in Priser og politikk i norsk historie, originally a lecture for the second Norwegian conference of historians.

[9] He also wrote about 400 pieces in the first edition of Norsk biografisk leksikon, a biographical dictionary which would become a preeminent source on important figures in Norwegian history.

He was decorated by France as a Knight of the Legion of Honour, and in 1952 he received the Gunnerus Medal from the Royal Norwegian Society of Sciences and Letters.

[38] Koht's father introduced his son to politics, taking him to the Liberal Party national convention in 1891, where he was allowed to enter since he studied at the university.

[23] While living in the United States, he developed a form of historical materialism, which led to a fusion of history scholarship and political views.

[50] In 1936 Koht expressed great concern for the consequences of the arms race taking place in Europe, which he felt could easily lead to war.

The strict non-intervention policy promoted by Koht and Prime Minister Nygaardsvold was heavily criticised by forces within the Labour Party.

[54] On 19 September 1936, Koht attempted to have the League of Nations impose a ceasefire in Spain, to be followed by a popular referendum on the country's constitution.

Again requesting to be allowed to resign, Koht stayed after months of debating ended with the party giving the cabinet free rein to do what it saw as best with regards to trade with Franco.

Koht was clear from early on that Norway should remain neutral, but also that in the event of her being forced to enter the war it was critical that it was on the side of the British.

This, along with other incidents, and the lack of a firm Norwegian response, led the warring parties to the impression that Norway could or would not effectively protect her neutrality.

[60] On 5 April the Allies sent notes to both Norway and Sweden warning that they would take any action necessary if the Germans were allowed to use the neutral countries' territory to their advantage.

Koht responded with a speech in which he said that the Allies had nothing to gain by interfering with Norwegian shipping lanes—the British had a more significant trade with Norway than the Germans.

Shortly before the mining was carried out, Koht warned the British that no further neutrality violations would be tolerated, and that in the future the Norwegians would respond with force.

[63] At the advent of the Nazi German Operation Weserübung, the invasion of Norway of 9 April 1940, Germany sent the envoy Curt Bräuer to present demands of capitulation.

[65] When the rest of the government fled from Molde to Tromsø, landing on 1 May, Koht and Ljungberg (Minister of Defense) continued from there with the cruiser HMS Glasgow to London.

[68] In response to the Allied decision to evacuate, the cabinet sent Koht to Luleå in Sweden to try to reinvigorate a previously rejected plan to create a demarcation line between the Germans and Norwegian in Northern Norway.

During a meeting with the Swedish minister of foreign affairs, Christian Günther, who was to act as a middle man with Germans in relation to the plan, Koht revealed that the Allies were about to evacuate Norway.

[8] Koht was granted leave of absence on 19 November 1940, and ultimately left the post of Minister of Foreign Affairs on 20 February 1941,[47] being succeeded by Trygve Lie.

[9] He became a board member of the Landsmål-based publishing house Det Norske Samlaget, and edited the Landsmål periodical Syn og Segn from 1901 to 1908, until 1905 together with Rasmus Flo.

[1] Koht's first travel abroad was in 1890, when he accompanied his father as well as Hans Jacob Horst and John Theodor Lund to an interparliamentary peace conference in London.

Historian Nils Ivar Agøy had noted that the socialists who were active in the bourgeois peace movement—the most prominent being Koht, Adam Egede-Nissen and Carl Bonnevie—were "radicalised sons of the bourgeoisie".

[70] Despite not holding the professor chair any longer, Koht continued his academic writing; his principal work from the post-war epoch was the six-volume Kriseår i norsk historie.