The prime minister of Portugal heads the government and manages the nation's affairs on a daily basis. The prime minister chooses or approves cabinet ministers and directs or coordinates their actions. The office thus differs from that in Britain, where the prime minister is the first among equals. Moreover, the entire cabinet bears responsibility for its actions, not the prime minister alone. The prime minister also directs the operations of the armed forces, although the president is formally the commander in chief. In other matters as well, the prime minister is autonomous, and the president has no right to direct the prime minister's policies.

Unlike the president, the prime minister is elected indirectly. As in other parliamentary systems, the prime minister is the leader of the largest party in the parliament or the head of a coalition of parties. The prime minister's term may last for up to four years, through an entire legislative period, after which time new elections. However, the prime minister may call earlier elections. The prime minister may ask for a vote of confidence from the parliament, but he could also be ousted by a vote of no confidence or through a leadership change in his own party. If a prime minister proves incompetent, loses support, or fails to provide needed national direction, the president may also request that a new government be formed.

In the ten years following the Revolution of 1974, Portugal was governed by nearly a dozen weak and short-lived governments, but the number of prime ministers was not large because all but two of them headed more than one cabinet. After mid-1985, however, the political system attained a greater stability when Aníbal Cavaco Silva, head of the Social Democrat Party (Partido Social-Democrata--PSD), formed first a minority government and then a majority government that lasted the whole 1987-91 legislative period. After his party won 50.4 percent of the vote in the 1991 national elections, Cavaco Silva formed another government that enjoyed an absolute parliamentary majority.

Data as of January 1993