Speaking from the Brazilian capital, Brasilia, New Zealand Embassy First Secretary Jeff Langley said all six were also found guilty of simple armed robbery.
But a third charge relating to a shot that grazed one of the Seamaster's crew as the bandits were leaving the boat was dismissed.
They all have five days in which to decide whether to appeal against the sentence.
Although the men confessed within days of Sir Peter's death on the Amazon last December, a federal judge had been deciding whether the charge they all faced of latrocinio (armed robbery leading to death) was appropriate.
The judge last week disallowed defence claims that the ringleader Tavares, who fired the two fatal shots into the back of the skipper, was mentally ill at the time.
Blake, 53, was shot dead on Dec. 5 last year by pirates who boarded his sailing vessel Seamaster, anchored at the mouth of the Amazon River in Brazil's poor northern state of Amapa. Seamaster had just completed an expedition up the Amazon and was due to leave Brazil within days.
Commenting during sentencing, which began about 7am today NZ time, Judge Linhares refuted the claim by some of the accused that Sir Peter fired the first shot.
He based his ruling on evidence from the crime scene and the sequence of events apparent in court testimony.
The judge also affirmed that, given the nature of the armed invasion of the Seamaster, there was no scope under Brazilian criminal law for the accused to claim "self-defence" in the face of the crew reaction.
He said it was "absolutely impossible" to characterise Sir Peter's reaction to the situation as "unfair" when faced with an "arbitrary and illicit" attack. Sir Peter, he said, could claim "legitimate defence of himself and his companions".
Defence suggestions that Sir Peter would not have been killed if he had not reacted as he did were "absolutely unacceptable, pure conjecture and vain speculation".
The killing of the top sportsman, who twice led New Zealand to victory in the America's Cup, shocked the world and exposed the lawlessness that rules parts of the Amazon forest, which covers an area bigger than Western Europe.
Last month Tavares attempted to dig his way out of jail in Macapa but was caught before he could leave the prison grounds.
Peter Blake, 1948-2001