Former Niger Delta militant Edmund Ebiware was jailed for life on Friday after being found guilty of helping to plan two car bombs in Nigeria's capital Abuja in 2010.
The verdict comes four days after the suspected mastermind of the deadly attacks, Henry Okah, was found guilty in a South African court of conspiracy to commit terrorism and detonating explosives.
Ebiware was convicted of treason and terrorism after being accused of communicating with Okoh before the explosions that killed at least 10 people during Independence Day celebrations.
"It is my judgment that the prosecution ... has proved the case beyond reasonable doubt. The accused is hereby found guilty as charged," Justice Gabriel Kolawole told an Abuja court.
Ebiware will be entitled to parole after 32 years, subject to good conduct.
Okah denies he ever led the Movement for the Emancipation of the Niger Delta (MEND). He moved to South Africa after Nigeria issued an amnesty for MEND members in 2009, lifting charges of gun-running and treason against him.
MEND's attacks on oilfields and pipelines across the swampy region that is home to Africa's biggest oil and gas industry cost Nigeria $1 billion a month in lost revenues at its peak, according to the central bank.
(Reporting by Camillus Eboh; Writing by Joe Brock)