The Federation of International Human Rights (FIDH) said it had confirmed through local rights activists that the three critics were convicted sometime in early April.
All three had written comments critical of Laos on their Facebook pages while working in neighbouring Thailand and had participated in protests outside Vientiane's embassy in Bangkok, the statement said.
They were arrested on their return to Laos in March last year.
Lodkham Thammavong, a woman believed to be in her early 30s, received a 12 year-prison sentence, FIDH said.
"By locking up dissidents for up to two decades, the Lao government has abandoned any pretense of compliance with the country's international human rights obligations," FIDH president Dimitris Christopoulos said in the statement.
Amnesty International had previously described the trio's lengthy pre-trial detention as an "enforced disappearance".
They were paraded on state television in May 2016 in prison uniforms where they made confessions saying they had harmed "national security".
Foreign journalists are not allowed in without a government minder while the party, which is dominated by elderly former Cold War-era guerilla fighters, retains full control over local media.
Critics are routinely jailed while others have simply disappeared.
Freedom House rates Laos as being one of the world's least free countries, on a par with countries like Saudi Arabia and Bahrain.
An email from AFP to the ministry of foreign affairs in Vientiane seeking further details went unanswered on Tuesday.
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