Cambodia was a constitutional monarchy from 6 May 1947 until 9 October 1970, when Marshal Lon Nol formally established the Khmer Republic. On 30 April 1972, a new constitution was passed by a national referendum. It provided for a directly elected president and a bicameral legislature consisting of an elective 126-member National Assembly and 40-member Senate. Upon the surrender of the Lon Nol government to insurgent forces on 17 April 1975, rule by the Royal Government of National Union of Kampuchea (Gouvernment Royal de l'Union Nationale de Kampuchea—GRUNK) was installed in Phnom Penh, with Prince Norodom Sihanouk as titular head of state. A new constitution, effective 5 January 1976, provided for a unicameral, 250-member People's Assembly, elected for a five-year term by universal suffrage of citizens over age 18. The PRK government, installed in January 1979, enacted a new constitution in June 1981. Under this constitution, an elected National Assembly was the supreme organ of state power; it was headed by a 7-member Council of State, which the Assembly elected from among its own members.
On 23 October 1991 the UN peace accord was signed by Cambodia's four factions. From May 23–28, 1993 a six-day election, the first multiparty election in more than 20 years, was held to determine the 120 members of the National Assembly. FUNCINPEC took 45.5% of the votes amounting to 58 seats in the assembly; the Cambodian People's Party (CPP), formerly the Kampuchean People's Revolutionary Party (KPRP), received 38.2% of the votes equaling 51 assembly seats; and Buddhist Liberal Democratic Party (BLDP) had 3% of the votes giving them 10 seats; and Moulinaka (Movement for the Liberation of Kampuchea, a pro-Sihanouk group formed in 1979 by Kong Sileah, considered an offshoot of FUNCINPEC) took one seat. This newly elected National Assembly was authorized to draft a constitution. In June 1993 FUNCINPEC and the Cambodian People's Party agreed to joint control of the defense and interior ministries, while FUNCINPEC controlled the foreign and finance ministries; Hun Sen and Prince Ranariddh served as co-chairmen of the interim government. The National Assembly ratified a new constitution on 21 September 1993. The monarchy was reestablished and commitments to liberal democracy, the rule of law, and women's rights were included. Prince Norodom Sihanouk ratified the constitution and again became King of Cambodia. The government of the State of Cambodia was an extremely fragile coalition after the elections, with enormous rivalries between Hun Sen's CPP, and Ranariddh's FUNCINPEC, as well as opposition from Sam Rainsy's unrecognized Khmer Nation Party. Much of the tension centered on attempts to win over factions of the Khmer Rouge, which were "coming out of the cold" en masse, their fighters and votes up for grabs by the rival political parties. In July 1997 Hun Sen's forces defeated FUNCINPEC in a brief but violent coup d'etat. In 1998, the number of seats in the National Assembly was increased to 122. July 1998's national election legitimized Hun Sen's CPP dominance of the nation, but FUNCINPEC won a high percentage of seats as well, and Ranariddh became Speaker of the National Assembly. The CPP took 64 seats, FUNCINPEC held 43, and the Sam Rainsy Party (SRP) took 15 seats in the National Assembly.
In March 1999, amendments to Cambodia's 1993 constitution allowed the formation of an unelected 61-seat Senate. Two Senate seats are appointed by the king, two elected by the National Assembly, and 57 are elected by "functional constituencies." Members serve five-year terms. Parliamentary elections were set for 27 July 2003.