Ilukamba, a career politician and Kabila ally, was previously the head of the DRC’s national railway company.
He also served as finance minister under former President Mobutu Sese Seko, who for more than three decades headed a corrupt and dysfunctional administration.
His appointment comes almost five months after Tshisekedi was declared the winner of a December 30 election which observers said was marred by irregularities and opponents denounced as rigged.
Tshisekedi beat Kabila’s hand-picked candidate Emmanuel Ramazani Shadary and rival opposition candidate Martin Fayulu, among others, in the presidential ballot.
Fayulu came in a close second but rejected the result and accused Tshisekedi of making a secret deal with Kabila to deprive him of victory. Tshisekedi and Kabila denied that there was a deal.
Kabila’s Common Front for Congo coalition dominated concurrent legislative elections, winning 342 of the 485 seats in the DRC’s parliament.
In March, the pair issued a joint statement confirming “their common will to govern together as part of a coalition government”. The DRC’s constitution dictates that the prime minister must come from the majority bloc in parliament, while the president traditionally makes the final decision on who will fill the post.
Kabila governed the largely impoverished but mineral-rich Central African country for 18 years before leaving office.
His final two years in charge saw him stay beyond the maximum term limit permitted by the DRC’s constitution and instead oversee a crackdown on protesters calling for him to quit.
Thousands of supporters turned out to welcome Katumbi’s arrival at the airport in Lubumbashi, the main city in his political heartland in the copper-mining Katanga region.
“I’m happy to be back home, the truth always triumphs,” Katumbi said.
Tshisekedi has pardoned 700 prisoners including several political opponents of Kabila since coming to power.
His supporters have claimed the moves point to a new era of political openness in the DRC after years of suppression of opposition figures.