The court of Additional District and Session Judge J S Sidhu pronounced the sentence in the high security Burail jail in Chandigarh where Jagtar Singh Tara is currently lodged, his counsel Simranjit Singh said.
A fine of Rs 35,000 was also imposed on Tara by the court, he said.
The lawyer said his client would not challenge the order in the higher court. "Jagtar Singh Tara told the court that he does not regret killing Beant Singh, he also said that, 'I have been fighting the battle of Sikhs' freedom against the govt & will continue to do so'," the lawyer was quoted by ANI.
Jagtar Singh Tara had confessed to his involvement in the assassination of Beant Singh in 1995, in a confession letter which he had submitted to the court in January this year.
On August 31, 1995, then chief minister Beant Singh was killed in an explosion outside the Civil Secretariat in Chandigarh. Sixteen others also lost their lives in the incident. Punjab police employee Dilawar Singh had acted as a human bomb in the incident.
Jagtar Singh Tara was arrested in September, 1995 in Delhi. However, he and two other accused escaped from Burail jail during the trial of the case in 2004.
He was later arrested from Thailand in 2015.
(wit inputs from agencies)