Bemba was found guilty earlier this year of war crimes and crimes against humanity, and jailed for 18 years.
On Wednesday he was convicted of corruptly influencing witnesses and falsifying evidence in that trial. Four close aides were also found guilty.
It is the first such corruption trial in the history of the ICC in The Hague.
The court heard that Bemba and his co-defendants had tried to corrupt 14 key witnesses in the original trial by bribing them with money and laptops.
Delivering the verdict, Judge Bertram Schmitt said the case was "about clear, and downright criminal behaviour of the five accused... that resulted in serious offences against the administration of justice".
"No legal system in the world can accept the bribing of witnesses, the inducement of witnesses to lie or the coaching of witnesses. Today's judgement sends a clear message that the court is not willing to allow its proceedings to be hampered or destroyed," he said.
Also found guilty were Bemba's lawyer Aime Kilolo; his legal case manager Jean-Jacques Mangenda; Congolese politician Fidele Babala; and Narcisse Arido, who had been a witness for the defence.
Bemba was convicted in March of crimes committed in the neighbouring Central African Republic (CAR) in 2002-2003. He was accused of failing to stop his rebel forces from killing and raping people.
Bemba was jailed in June and is appealing against his conviction.
In the latest case, prosecutors had said evidence including telephone recordings, records of money transfers, emails and texts showed Bemba and his aides had tried to pervert the course of justice.
The defence, however, argued that the telephone recordings had been misinterpreted.
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Former Congolese Vice President Jean-Pierre Bemba has been found guilty by the International Criminal Court (ICC) of bribing witnesses.