Bemba, who served as vice president from 2003 to 2006, had been jailed by the International Criminal Court over crimes committed by rebels under his command, but the court overturned his sentence in 2018.
The Democratic Republic of Congo is struggling to quell an armed rebellion by the M23 insurgency, which Kinshasa and several Western governments say is backed by neighbouring Rwanda.
Tshisekedi's former chief of staff, Vital Kamerhe, was appointed as minister of economy, after he was sentenced to 20 years in prison for embezzlement before being acquitted last year.
A spokeswoman for Tshisekedi appeared on national television early Friday to read out the composition of the new government.
The country is due to go to the polls in December.
Tshisekedi, who has been in power since January 2019, has said that he will run for re-election.
Former DRC Militia Boss Named Defense Chief
FILE: Then-leader of the Democratic Republic of Congo's political party Movement for the Liberation of the Congo (MLC) Jean-Pierre Bemba greets the crowd of supporters as he returns to DR Congo on June 23, 2019 in Kinshasa.
KINSHASA - DRC President Felix Tshisekedi has appointed former militia leader Jean-Pierre Bemba as minister of defense in a cabinet reshuffle on Friday, as the country grapples with armed conflict in its restive east.