Alain Ononino, Cameroon law enforcement chief at the World Wide Fund for Nature, said Symphorien Sangha was also fined $43,000 at Tuesday's sentencing.
He was found guilty on Monday of killing elephants and assaulting a forest ranger.
On Friday, the same court is expected to hand down a verdict against Sangha's twin brother, Rene Sangha, who is accused of collaborating on the poaching activity that dates back to at least 2006.
Ononino said the cases showed how regional governments have ramped up efforts to combat poaching that has been devastating elephant populations in Central Africa for decades.
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