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. However, after the Chilean coup of 1973, Congress was dissolved on September 21 and Zaldívar went into exile with his family in Spain. Returning to Chile the following year, Zaldívar became president of the Christian Democrat Party, from 1975 to 1982.