During his study he became involved in the movement to politically organise the college students, and in publishing a periodical, the Kweekelingenbode, of which he became the editor in 1908.

He also met his future wife, the teacher Henriëtta Johanna Wilhelmina Schoemaker, whom he married on 9 October 1915.

The leadership of the SDAP was keen to encourage this development and Banning was elected a member of the party's governing body in 1931, and of its executive committee in 1935.

However, he resigned from the executive committee in protest of the decision to formally abolish the party's pacifist stance in 1937, in reaction to the rise of Nazism as a force that threatened Dutch democracy.

[Note 2] He remained a member of the governing body until 1939 when he became editor of the party's ideological publication Socialisme en Democratie (Socialism and Democracy).

This group of anti-Nazi politicians used their internment to plan a political reform of the Dutch party system for the post-war period.

[1] Immediately after Liberation in 1945 Banning, together with a number of other politicians of different parties, such as Willem Schermerhorn, Piet Lieftinck, Jan de Quay, E.M.J.A.

Sassen, and Hendrik Brugmans, formed the Nederlandse Volksbeweging as a movement to bring about what was called the Doorbraak (Breakthrough) of the Pillarisation system.

[1] Though the hoped for doorbraak did not take place, the PvdA played a major role in the post-war part of Dutch 20th-century political history, and Banning for a while became its "house ideologue" as editor of Socialisme en Democratie.

[1] Already during his internment in the Second World War Banning, under the influence of his fellow hostage Brugmans, had become interested in the philosophy of personalism, as developed by the circle around the French literary periodical Esprit.