He published a poetry collection in 1922 called Blod ("Blood"), containing poems on the themes of misery and poverty as well as tabooed topics such as prostitution and necrophilia, was considered scandalous and confiscated by the authorities (re-published in 1968).
[2] He joined the Communist Party of Denmark (DKP) and became one of the key personalities behind several Danish left-wing journals such as Monde, Plan and Frem.
Broby-Johansen ended his political activism in 1935, following the exile of Leon Trotsky and the persecution of Trotskyism in the Soviet Union, and he focused on artistic work.
As art historian, he was also responsible for the reconstruction of the colouring of the copy of the greater Jelling stone commissioned in the 1930s, which he dubbed "Denmark's baptismal certificate".
He returned to political activism in the 1960s in support of Maoism and the Chinese Cultural Revolution, and in the 1970s he campaigned against the accession of Denmark to the European Communities.