Following the promulgation of a new constitution in 1990, Sao Tome and Principe held multiparty elections for the first time since freedom. Shortly after the constitution took effect, the National Assembly formally legalized opposition parties. Independent candidates also were permitted to participate in the January 1991 legislative elections. The National Assembly is the supreme organ of the state and the highest legislative body. Its members are elected for a 4-year term and meet semiannually.

The president of the republic is elected to a 5-year term by direct universal vote and a secret ballot, and may hold up to two consecutive terms. Candidates are chosen at their party's national conference or individuals may run independently. A presidential candidate must obtain an outright majority of the popular vote in either a first or second round of voting in order to be elected president. The prime minister is named by the president but must be ratified by the majority party and thus normally comes from a list of its choosing. The prime minister, in turn, names the 14 members of the Cabinet. The National Assembly is made up of 55 members, all of whom must stand for reelection every 5 years.

Justice is administered at the highest level by the Supreme Court. Formerly responsible to the National Assembly, the judiciary is now independent under the new constitution.

Administratively, the nation is separated into seven municipal districts, six on Sao Tome and one comprising Principe. Governing councils in each district maintain a limited number of autonomous decision-making powers, and are reelected every 5 years.