The six men have been in a Calcutta jail for more than four years and have protested their innocence throughout their trial.
They had earlier been convicted of smuggling weapons, after several crates of arms, apparently meant for a militant Hindu sect, were parachuted out of a transport aeroplane over West Bengal.
But they were found not guilty of waging war against India - the charge that carries the death penalty.
The six men have been in a Calcutta jail for more than four years and have protested their innocence throughout their trial.
It emerged in court that Bleach had informed the British authorities after he was approached about an apparently illegal delivery of weapons, and they in turn informed India.
But the drop went ahead and a week later, Indian air force jets forced down the Antonov 26 transport plane which made the drops.
Bleach said he was "very disappointed, but not surprised" after receiving his sentence, and promised to appeal.
As he was being led from the dock he said: "I was unaware that you could be convicted on the basis of proven false evidence in the Indian courts.
"On that basis, I shall appeal immediately. The guilty verdict is a travesty by any standards."
'James Bond activities'
British Conservative MP Sir Teddy Taylor, who has supported Bleach's claims that he was working with British intelligence, said: "I have been more appalled by this case than any other in 35 years in Parliament.
"Peter has been involved in James Bond-style activities. But the court was not told he had been in touch with the British authorities.
"I am sure if all the evidence had been given to the courts it would have been a much lesser sentence."
After Bleach was found guilty last week, Sir Teddy called on UK Home Secretary Jack Straw to open secret service files on the case to the Indian authorities.
'Unexplained mystery'
Prosecution lawyers said weapons on board - which included AK-47 assault rifles, rocket launchers, anti-tank grenades and thousands of rounds of ammunition - were intended for a religious cult in Bengal, the Ananda Marg.
The men were arrested several days later as they flew across India from Thailand.
The judge rejected an appeal for clemency from the Latvian crew.
The man alleged to have masterminded the entire operation, a Dane who uses the alias Kim Davy, has so far evaded Indian investigators.
But India's Central Bureau of Investigation admits that the mystery of the arms drop will continue to persist, according to BBC Calcutta correspondent Subir Bhaumik.
The CBI says Bleach and the Latvians merely carried out the drop in keeping with the instructions of Kim Davy.
Officials say that unless he is caught or surrenders and speaks up, it will never be clear who really planned the arms drop and who the weapons were actually meant for.
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