Tonga became a constitutional hereditary monarchy in 1875. The King has highest executive authority in the Privy Council. Under him is a Prime Minister as Head of Government and a Deputy Prime Minister, both elected by and from the members of parliament and appointed by the monarch. The Cabinet is made up of 12-14 ministers, including the Prime Minister as well as the Governors of Ha'apai and Vava'u, ex officio members of the Cabinet. The ministers and governors are appointed by the King, and these are appointments for life, with exceptions. The Legislative branch is made up of the Legislative Assembly, or Fale Alea, who serve four-year terms. The Judiciary is made up of the Privy Council, Court of Appeal, Supreme Court, Land Court and Magistrates' Court.

Currently, there has been political reform resulting from movements that began in the 1990s with the Tongan Pro-Democracy Movement (TPDM) demanding the powers of the monarchy be curtailed. After King Taufa’ahau Tupou IV’s death in 2006, there were violent and destructive riots as a result of the king’s authoritarian rule. The new king expresses support for political reform and several things have shown this to be sincere. In February 2006, Prince 'Ulukalala Lavaka Ata resigned as prime minister and the first commoner prime minister, People's Representative Feleti Sevele, was appointed by the King. In 2009, a Constitutional and Electoral Commission (CEC) was set up and in November 2009 was debated by the Legislative Assembly with the result that, from 2010, there was an increase in the number of people’s representatives, most Assembly members were elected and the king surrendered power to the Prime Minister.

Local government is managed through popularly elected town and district officials. Each town official represents the central government in the villages; the district official has authority over a group of villages.

Regionally, Tonga is member of the Pacific Islands Forum (PIF) and the Secretariat of the Pacific Community. Internationally, it is a member of the United Nations, the World Trade Organization and the African, Caribbean and Pacific Group of States.