A former vice president turned opposition leader, Bemba filed his candidacy for much-delayed polls now slated for December to replace President Joseph Kabila, whose mandate ran out in 2016. Kabila has yet to commit to stepping down.
Bemba, whose war crimes convictions at the International Criminal Court (ICC) were quashed on appeal in May, touched down at Kinshasa's N'Djili airport where thousands of cheering supporters wore T-shirts, hats, scarves and robes bearing his image.
The former warlord's return is expected to energise the opposition to Kabila, who has been in power since his father's assassination in 2001 and is barred by constitutional term limits from standing for a new term.
>>Jean-Pierre Bemba: From convicted warlord to exonerated hero of Congo
Kabila has refused to commit publicly to not contesting the election. That has kept the country in suspense over whether he will choose someone else to represent his ruling coalition, paving the way for Congo's first democratic transition, or try
to run again and risk a violent backlash.
Security forces have killed dozens of protesters since late 2016 when Kabila refused to step aside at the end of his mandate, saying elections needed more time to be organised. Militia violence in the eastern borderlands has surged since
>> Video: Victims of Bemba's militia indignant over his return to DR Congo
Bemba said last week that he believes he is the strongest candidate to represent the opposition but would be willing to cede his place in favour of another candidate.
He could also see his eligibility to run challenged in the courts. The ruling coalition said last week he was disqualified from running by a witness-tampering conviction at the ICC even though the convictions for murder, rape and pillaging committed by his militia in neighbouring Central African Republic in 2002 were thrown out.
The invalidation of Bemba's candidacy would infuriate his supporters, especially in western Congo. His loss to Kabila in the 2006 election saw gunbattles erupt in the streets of Kinshasa between his militiamen and government troops.
(FRANCE 24 with REUTERS)