Situated on the radical wing in the 1910s, he was among the architects as the Labour Party denounced the Twenty-one Conditions in 1923 and reunited with the social democrats in 1927.

He was the deputy party leader from 1923 to 1932, and served as Norwegian Minister of Foreign Affairs in Hornsrud's short-lived cabinet in 1928.

He was born on 4 December 1881, in Kristiania as the son of chief physician Edvard Isak Hambro Bull (1845–1925) and his wife Ida Marie Sofie Paludan (1861–1957).

[1] Bull finished his secondary education in 1899, and studied in classical philology, geography and history at the University of Kristiania.

His main work in the field, volume two of Det norske folks liv og historie, was published as late as 1931.

Bull was also known as a co-editor of the biographical dictionary Norsk biografisk leksikon,[1] the first volume of which was released by the publishing house Aschehoug in 1923.

Publications in this vein include Karl Marx (1918) and Den russiske arbeider- og bonderevolution (1922).

[1] While studying, Bull became acquainted with radical politicians like Emil Stang, Jr., Jakob Friis and Kyrre Grepp.

Bull was a staunch opponent of the Twenty-one Conditions, and following a resolution at the February 1923 national convention, the Labour Party left the Comintern.

[7] He was both preceded and succeeded by people who were also Prime Ministers; Ivar Lykke and Johan Ludwig Mowinckel.

Historians generally agree that from this point, the Labour Party decisively drifted away from the revolutionary rhetoric and policies.

This meant that he did not release further volumes of Det norske folks liv og historie, as he had planned.