Sarsenbaiuly's supporters had alleged that he was the victim of a political assassination, however the court backed prosecutors who said Yerzhan Utembayev, a former civil servant, had ordered the killing to settle a personal score.
Judge Lukmat Merekenov handed out a sentence of 20 years to Utembayev for ordering the murder.
Ex-policeman Rustam Ibragimov, who prosecutors said directly organised the murder, was sentenced to death but this will be automatically commuted to life imprisonment as Kazakhstan has a moratorium on capital punishment.
One other defendant was given 20 years in prison, while the remaining seven were sentenced to between 10 and 14 years. Prosecutors said they were accomplices in the murder.
Sarsenbaiuly, a member of the Nagyz Ak Zhol party, was a former government minister and ambassador to Russia and a high-profile opponent of Nursultan Nazarbayev, president of Kazakhstan.
In February, gunmen abducted him along with his bodyguards from the country's commercial capital, Almaty. The men's bodies were later found in nearby mountains with gunshots to the back of their heads.
Prosecutors said Utembayev ordered the killing in revenge for a newspaper article published three years before the murder in which he was branded a drunk.
However, opposition supporters said the investigation and trial were biased, incomplete and rife with violations and have called for a broader probe including the questioning of President Nazarbayev and other top officials.
The killing provoked a wave of protests which, though small, were unusual for Kazakhstan, an oil-rich Central Asian nation whose leaders pride themselves on the country's political stability.
Nazarbayev, who has ruled the former Soviet republic for 16 years, won elections last December, however the results were criticised by western observers who cited ballot-stuffing, multiple voting, interference, media bias and intimidation.