In the 1920s he organized Vientirauha, a strikebreakers' organisation, in Southern Ostrobothnia. He made a speech at the first meeting of the anti-communist Lapua Movement as it was organized in 1929, and was chosen as its leader as the movement radicalized in the following year. He took part of the abortive Mäntsälä Rebellion of 1932 that ended with the dissolution and banning of the Lapua Movement and the brief imprisonment of Kosola.
Kosola was chosen as president of the Lapua Movement's successor, the Patriotic People's Movement, but as the Movement became more political, Kosola had less time to participate in its affairs in Helsinki.
Kosola's radical right-wing politics caused a common saying in the 1930s: "Heil Hitler, meil Kosola," accented Finnish for "They've got Hitler, we've got Kosola". Sometimes also a third stanza, "muil Mussolini" (the others' Mussolini) was added. Kosola had a sobriquet Kosolini after his charismatic and vivid style of speech similar to Benito Mussolini.