The National Assembly approved the appointment with all 125 members voting in favor without any debate. Hun Sen's Cambodian People's Party won a July 29 general election by a landslide, but critics consider the polls unfree and unfair because the only credible opposition grouping, the Cambodia National Rescue Party, was dissolved by court order last year in an action seen as politically motivated.
The 66-year-old Hun Sen has been in power for 33 years, combining guile and strong-arming to dominate his country's politics. He declared before the election that he intended to serve two more terms at the helm.
A crackdown on critics and opponents was launched after the 2013 general election and local elections last year showed a softening of support for Hun Sen's ruling party. The founding leader of the now-defunct Cambodia National Rescue Party is in self-imposed exile and his successor in prison awaiting trial on what is widely seen as a trumped-up charge of treason.
In a speech at the assembly's opening session on Wednesday, King Norodom Sihamoni conveyed his warmest congratulations to the new lawmakers and urged them to fulfill their duties under the law and to work for the benefit of the entire country. However, in a sign of continuing international rejection of the election process, no representatives from the U.S., British and Australian embassies attended the event. Many other diplomats also appeared to be absent.
The United States in December imposed visa restrictions on top Cambodian officials because of the anti-democratic actions taken in the lead-up to the vote , and said it was disappointed by the "flawed elections."
Hun Sen has aligned his country firmly with China in recent years, both politically and economically, allowing him to largely ignore criticism from the West, upon whom he used to depend for development assistance.
Hun Sen was a member of the radical communist Khmer Rouge during its successful five-year war to topple a pro-American government, then defected to Vietnam during Khmer Rouge leader Pol Pot's 1975-79 genocidal regime that left nearly 2 million Cambodians dead.
He became prime minister in 1985 in a Vietnamese-backed single-party communist government and led Cambodia through a civil war against the Khmer Rouge, which eased off with the 1991 Paris Peace Accords that also installed a democratic political framework.