In a double coup, first military right-wingers opposing Alessandri seized power in September 1924, and then reformers in favor of the ousted president took charge in January 1925. The latter group was led by two colonels, Carlos Ibáñez del Campo and Marmaduke Grove Vallejo. They returned Alessandri to the presidency that March and enacted his promised reforms by decree. Many of these reforms were encapsulated in the new constitution of 1925, which was ratified in a plebiscite.

The 1925 constitution was the second major charter in Chilean history, lasting until 1973. It codified significant changes, including the official separation of church and state, which culminated a century of gradual erosion of the political and economic power of the Roman Catholic Church. The constitution also provided legal recognition of workers' right to organize, a promise to care for the social welfare of all citizens, an assertion of the right of the state to infringe on private property for the public good, and increased powers for the now directly elected president in relation to the bicameral Congress, in particular concerning the removal of cabinet ministers, which heretofore had often been removed at the whim of the legislature.

Presidential and congressional elections were staggered so that a chief executive could not bring a legislature in on his coattails. The new constitution extended presidential terms from five to six years, with immediate reelection prohibited. It established a system of proportional representation for parties putting candidates up for Congress. The government was divided into four branches, in descending order of power: the president, the legislature, the judiciary, and the comptroller general, the latter authorized to judge the constitutionality of all laws requiring fiscal expenditures.

The Office of Comptroller General of the Republic (Oficina de la Contraloría General de la República) was designed by a United States economic adviser, Edwin Walter Kemmerer. In 1925 he also created the Central Bank of Chile and the position of superintendent of banks, while putting the country on the gold standard. His reforms helped attract massive foreign investments from the United States, especially loans to the government.