In 1922 Bartel was elected a member of Poland's "Sejm" (parliament) and held this position until 1929. Initially, he was a member of the party PSL "Liberation", but he was not satisfied with the radicalization of the group. In March 1925 at the Congress of the Polish People's Party he decided to adopt, among others, a reform without compensation. Bartel eventually left the party and the organisation in April 1925, along with Marian Zyndram-Kościałkowski and Bolesław Wysłouch and later founded the parliamentary "Labour Club". This organization quickly came under the direct influence of commander-in-chief Józef Piłsudski. Just before the May Coup of 1926 Kazimierz Bartel received an order from Marshal Piłsudski to prepare for a take over as prime minister after the expected collapse of President Stanisław Wojciechowski and his government.