He was charged with offences of insult and incitement to commit offences, pursuant to Cambodia’s Criminal Code.
In addition to Rainsy, two other CNRP leaders living overseas, Ho Vann and Kak Komphear, were accused of the same offences.
The court also ordered Kong Mas and Roeun Kimlun to spend one year and six months behind bars for being in cahoots with Rainsy. At present, only Kong Meas is detained.
Last month, the Phnom Penh court ordered the arrest of Sam Rainsy, asking authorities to promptly look for, arrest and bring him to court for offending Cambodian King Norodom Sihamoni.