A Paris court said Mikel Kabikoitz Carrera Sarobe, 40, should spend at least 22 years in prison for firing the three shots that killed Raul Centeno Bayon and Fernando Trapero Blazquez in their vehicle while on assignment in the French town of Capbreton near the Spanish border.
Another accused, Saioa Sanchez Iturregui, 31, was sentenced to 28 years while a third, Asier Bengoa Lopez de Armentia, 37, was acquitted of the murder charges but handed a 15-year sentence for other charges.
Sanchez Iturregui was ordered held for a minimum two-thirds of her sentence, or about 19 years.
Shortly after the shootings, ETA said in a statement that the police had been killed during an "armed confrontation". But prosecutors said the two officers had not been armed when they were killed.
The three main suspects also faced kidnapping charges after allegedly taking a driver hostage and seizing her vehicle during their escape. The driver was released unharmed.
Four other alleged ETA members also on trial on charges of aiding the other suspects, though they were not suspected of direct involvement in the killings, received sentences of five to nine years, one in absentia.
ETA is blamed for 829 deaths in a four-decade campaign of bombings and shootings for independence for the Basque Country of northern Spain and southwestern France.
The organisation, classed as a terrorist group by the European Union and the United States, announced in October 2011 that it was giving up its armed struggle.
It has yet to formally disarm and the Spanish government has refused to hold talks with its leaders.