Bemba, who received a thunderous welcome in Kinshasa on August 1, is in the country to file his nomination for president.
Katumbi posted his message on twitter saying it was heartwarming to see Bemba return to the country of his ancestors to exercise his democratic right.
Bemba contested the 2006 presidential elections losing to Kabila and was later jailed for crimes against humanity at the International Court of Justice.
His recent release from prison was welcomed by Congolese people.
The exiled Katumbi is also due to return to the DRC to file his nomination. The deadline for nominations is August 8.
“Welcome back JP Bemba to the land of your ancestors,” he tweeted, adding “I share the joy of my compatriots.”
Katumbi says the outpouring of emotion by the Congolese people in welcome Bemba was testament DRC was ready for regime change.
“We share the emotions of our people. It was great. Very soon the people of DRC want to participate in a truly inclusive election,” he stressed.
Katumbi, the former governor of the mineral rich southern Katanga province, is a front-runner in polls conducted by international observers.
The owner of football club, TP Mazembe, has thus formally applied to the authorities to grant him rights to fly into the country aboard a private jet.
A letter sent to the civil aviation authorities date July 30th and signed by Katumbi requested that his jet be allowed to land on August 3rd at the Luano airport located in the city of Lubumbashi in southeastern Congo.
It adds that on board shall be six other allies of his. There has not been any response of an official acceptance or rejection of his request. Katumbi is looking to file his candidacy for the upcoming polls. The deadline for submission is August 8.
In an interview with South African media outlets, Katumbi held that he was returning home a ‘free man’ to participate in the political process. This is the firmest indication of his return after over a year in exile.
He was flown out to South Africa in 2016 for medical treatment after police teargassed his supporters during a court appearance in Lubumbashi. He ended up in Belgium for further treatment.
Since then, he has been shuttling between Europe and Africa seeking support for a peaceful and democratic transition in the Congo.
Incumbent Kabila’s mandate expired in December 2016 but he continues in office since polls for his successor has yet to be held. Kinshasa has used lack of a credible voters register and security concerns as basis for the postponements.