Stanis Bujakera, 33, has been jailed since September over an article in Jeune Afrique magazine that suggested Congolese military intelligence operatives had killed opposition politician Cherubin Okende the month before.
The article — which was unsigned — was based on an alleged confidential memo from a separate intelligence agency. Congolese authorities have said the memo is a fake.
A Kinshasa court found Bujakera guilty on charges including forgery and "spreading false rumors," and ordered the six-month sentence along with a fine of one million Congolese francs ($400). Prosecutors had asked Bujakera to be jailed for 20 years.
His arrest followed a Jeune Afrique article published in late August, which suggested that Congolese military intelligence had killed Okende the month before.
Okende, a former minister and spokesman for the opposition party Ensemble Pour la Republique ("United for the Republic"), disappeared on July 12 last year. His bullet-riddled body was found in his car in Kinshasa the following day.
The prosecutor's office announced on February 29 that an autopsy found Okende had committed suicide, an assertion his party called a "refusal of justice."
The trial came amid rising political tensions in the Democratic Republic of Congo in the run-up to last December's presidential and parliamentary elections.
President Felix Tshisekedi won a second five-year term after sweeping the election, which was branded a sham by the opposition.
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