Executive power is exercised by the government. Legislative power is vested in both the government and the two chambers of the National Congress. The Judiciary is independent of the executive and the legislature of Chile. 

The Constitution of Chile was approved in a national plebiscite in September 1980, under the military government of dictator Augusto Pinochet. It entered into force in March 1981. After Pinochet left power in the 1988, saying this country was ready to keep going along with a plebiscite, the Constitution was amended to ease provisions for future amendments to the Constitution.

 In September 2005, President Ricardo Lagos signed into law several constitutional amendments passed by Congress. These include eliminating the positions of appointed senators and senators for life, granting the President authority to remove the commanders-in-chief of the armed forces, and reducing the presidential term from six to four years while also disabling immediate re-election.

The bicameral National Congress (Congreso Nacional) consists of the Senate (Senado) and the Chamber of Deputies (Cámara de Diputados).

Chile's congressional elections are governed by a unique binomial system that rewards coalition slates. Each coalition can present two candidates for the two Senate and two lower-chamber seats apportioned to each chamber's electoral districts. 

Typically, the two largest coalitions split the seats in a district. Only if the leading coalition ticket outpolls the second-place coalition by a margin of more than 2-to-1 does the winning coalition gain both seats. 

The political parties with the largest representation in the current Chilean Congress are the centrist Christian Democrat Party and the conservative Independent Democratic Union (Unión Demócrata Independiente). The Communist Party and the small Humanist Party failed to gain any seats in the 1998 elections.

Elections are very labor-intensive but efficient, and vote counting normally takes place the evening of the election day. One voting table, with a ballot-box each, is set up for at-most 200 names in the voting registry. Each table is manned by five people (vocales de mesa) from the same registry. 

Vocales have the duty to work as such during a cycle of elections, and can be penalized legally if they do not show up. A registered citizen can only vote after his identity has been verified at the table corresponding to his registry. Ballots are manually counted by the five vocales, after the table has closed, at least eight hours after opening, and the counting witnessed by representatives of all the parties who choose to have observers.

The Senate is made up of 38 members elected from regions or subregions. Senators serve approximately eight-year terms.

The Chamber of Deputies has 120 members, who are elected by popular vote to serve four-year terms. The last congressional elections were held on December 11, 2006. The next congressional elections are scheduled for December 2009.

The current Senate composition is as follows: 20 seats are held by the Coalition of Parties for Democracy (CPD): Six Christian Democrats (PDC), eight Socialists (PS), three Party for Democracy (PPD) and three Social Democrat Radical Party (PRSD); 17 by the Alliance for Chile (APC): nine Independent Democratic Union (UDI) and eight National Renewal (RN); and one independent leaning right.

The current lower house—the Chamber of Deputies —contains 65 members of the governing coalition: 21 Christian Democrats (PDC), 15 Socialists (PS), 22 Party for Democracy (PPD) and seven Social Democrat Radical Party (PRSD); 54 from the center-right Alliance for Chile(APC): 34 Independent Democratic Union (UDI) and 20 National Renewal (RN); and 1 from the Independent Regional Force (FRI) coalition: 1 Regionalist Action Party of Chile (PAR).

Since 1987, the Congress operates in the port city of Valparaiso, about 110 kilometers (~70 mi.) northwest of the capital, Santiago. However some commissions are allowed to meet in other places, especially Santiago. Congressional members have tried repeatedly to relocate the Congress back to Santiago, where it operated until the Chilean Coup of 1973, but have not been successful. The last attempt was in 2000, when the project was rejected by the Constitutional Court, because it allocated funds from the national budget, which, under the Chilean Constitution, is a privilege of the President.

Chile's judiciary is independent and includes a court of appeal, a system of military courts, a constitutional tribunal, and the Supreme Court. The judges on the Supreme Court or Corte Suprema are appointed by the president and ratified by the Senate from lists of candidates provided by the court itself. The president of the Supreme Court is elected by the 21-member court.

Chile's legal system is civil law based. It is primarily based on the Civil code of 1855, derived from Spanish law and subsequent codes influenced by European law of the last half of the 19th Century. It does not accept compulsory ICJ jurisdiction.

From the year 2000 onward, Chile completely overhauled its criminal justice system; a new, US-style adversarial system has been gradually implemented throughout the country with the final stage of implementation in the Santiago metropolitan region completed on June 9, 2001