Mobanza Mobembo Gerard was found guilty of ivory trafficking and the attempted murder of park rangers.
Gerard, known as Guyvanho, led poaching expeditions which resulted in the deaths of hundreds of animals, according to the Wildlife Conservation Society.
The case has been held up as a milestone in the fight to hold wildlife criminals to account.
His trial and sentencing last week marked the first criminal conviction of a wildlife trafficker in the country.
Previously, environmental crimes were tried in civil courts and incurred a maximum sentence of five years, the WCS said.
The sentence “sends an extremely strong message that wildlife crime will not be tolerated and will be prosecuted at the highest levels,” WCS regional director Emma Stokes said in a statement on Monday.
Congolese judicial authorities could immediately be reached for comment.
The attempted murder charges against Gerard were connected to a 2019 incident when his poacher group allegedly fired at and wounded members of a ranger patrol in Nouabale-Ndoki National Park, WCS said.
The park covers 4,000 square kilometres (1,540 sq miles) in the north of the country.
Its dense lowland rainforest has been a refuge for the region's rare forest elephants, which were only confirmed to be a separate species from the larger African savannah elephant in 2010.
As recently as 1980, there were over a million elephants in Africa; they now number just over 300,000 and are at risk of being wiped out from all but the most heavily protected pockets.
In addition to ivory demand - mostly from China - persecution is increasingly being seen in areas where elephants come into contact with expanding human populations and settlements.
Earlier this year it was announced Botswana was auctioning licences to hunt a total of 70 elephants in seven districts, the first such hunting to take place since the country’s president, Mokgweetsi Masisi, lifted a five-year ban on big game hunting in May 2019.
Additional reporting by Reuters
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