The ruling will effectively dismantle the CNRP and also see 118 party members banned from politics for five years.
The Supreme Court of Cambodia has dissolved the Cambodia National Rescue Party (CNRP), the most popular opposition party in the country.
"Dissolving the main opposition party, coupled with a heavy-handed crackdown on the media and civil society, certainly looks like the move of a dictator - a frightened one", said Charles Santiago, a member of the Malaysian Parliament and chair of ASEAN Parliamentarians for Human Rights.
Cambodian police officials block a street during a hearing at the Supreme Court in Phnom Penh on November 16, 2017.
Kem Sokha was accused treason and plotting to overthrow the government with the support of the US, a move which led to a wider government crackdown on freedom of speech and civil society.
The Cambodian opposition party leader's oldest daughter Kem Monovithya, a high-ranking officials of the CNRP, called for global sanctions against the government.
So far, Hun Sen has shown no sign of backing down and in fact appears to be mounting his biggest assault on Cambodian democracy since the coup. It claimed that the party's leader, Kem Sokha, had colluded with the USA in the hope of overthrowing the ruling Cambodian People's Party (CPP).
Dozens of police manned barriers outside the court in the centre of Phnom Penh, a yellow-painted building ornamented with gold in traditional Cambodian style.
"Today marks the end of true democracy in Cambodia", said CNRP Vice President Mu Sochua, who fled Cambodia in early October.
According to the reports, Cambodia's Prime Minister, Hun Sen, has ruled for 32 years and has held a tight grip on power since ousting a co-prime minister in a bloody 1997 coup.
On Wednesday, Rainsy made an announcement that he would be returning to the CNRP, a party he quit in February over fears at the time that it would be dissolved if he remained a member of it. Life expectancy has risen from 50 to 70.
He called for governments to drop their recognition of the prime minister and "delegitimize the Hun Sen regime". US-linked groups like Voice of America, Radio Free Asia and the National Democratic Institute have also been forced to disband or leave the country.
More than half the CNRP's members of parliament had already fled Cambodia, fearing detention in a crackdown on Hun Sen's critics, civil rights groups and independent media that began previous year. It was taken off air in August but continued broadcasting through Facebook.
In that election - the official results of which were disputed by the CNRP - the opposition party managed to garner almost half of over 6 million votes cast to win 55 seats in the National Assembly, against 68 for the CPP.