The islands were first determined by Portuguese navigators between 1469 and 1472. The first successful settlement of Sao Tome was accomplished in 1493 by Alvaro Caminha, who received the land as a grant from the Portuguese crown. Principe was settled in 1500 under a similar arrangement. By the mid-1500s, with the help of slave labor, the Portuguese settlers had turned the islands into Africa's foremost exporter of sugar. Sao Tome and Principe were taken over and administered by the Portuguese crown in 1522 and 1573, respectively.

In 1990, Sao Tome became one of the first African countries to embrace democratic reform and changes to the constitution--the legalization of opposition political parties--led to elections in 1991 that were nonviolent, free, and transparent. Miguel Trovoada, a former prime minister who had been in exile since 1986, returned as an independent candidate and was elected president. Trovoada was re-elected in Sao Tome's second multiparty presidential election in 1996. The Party of Democratic Convergence (PCD) toppled the MLSTP to take a majority of seats in the National Assembly, with the MLSTP becoming an valuable and vocal minority party. Municipal elections followed in late 1992, in which the MLSTP came back to win a majority of seats on 5 of 7 regional councils. In early legislative elections in October 1994, the MLSTP won a plurality of seats in the Assembly. It regained an outright majority of seats in the November 1998 elections. The Government of Sao Tome fully functions under a multiparty system. Presidential elections were held in July 2001. The candidate backed by the Independent Democratic Action Party, Fradique de Menezes, was elected in the first round and inaugurated on September 3. Parliamentary elections held in March 2002 led to a coalition government after no party gained a majority of seats.