Because the actors, who have been incarcerated since their arrest in August 2014, confessed to the crime, their sentences have been cut to two-and-a-half years.
Sentencing took place at a Bangkok court under Thailand's "Lèse-majesté" laws.
Saraiyaem and Mankong performed A Wolf's Bride only once, on Oct. 13, 2013, at Thammasat University; however, that performance was subsequently distributed via social media.
Although the pair do not plan to appeal the sentencing, they can seek a royal pardon.
The current king, Bhumibol Adulyadej, is descended from Mongkut, portrayed as the main character in the musical The King and I, and his son, King Chulalongkorn.
Rupert Abbott, Amnesty International’s research director for Southeast Asia and the Pacific, said in a statement, "This is an assault on freedom of expression. It is appalling that Patiwat Saraiyaem and Pornthip Mankong have been jailed just for staging a play. Since taking power last year, Thailand’s military authorities have made unprecedented use of the lèse-majesté law to silence and target critics who are simply peacefully exercising their human rights.
"The pair should never have had to stand trial in the first place, and the verdict should be overturned and sentences expunged. Their guilty plea should not be considered as an admission of criminal responsibility as the courts regularly reduce sentences for defendants who have pleaded guilty."