In 1973, Zaldívar for the first time became a member of the National Congress of Chile, upon election to the Senate of Chile for the Second Provincial District of Atacama and Coquimbo, joining the Economic Committee of Congress.
In exile, Zaldívar was made President of the International Christian Democrats, an international organization of political parties, from 1981 to 1986, when he became a member of its advisory council.