The verdict paves the way for Tshisekedi to serve another five years as head of Africa's second-largest country and the world's top producer of cobalt and other prized industrial commodities.
The Constitutional Court validated the incumbent's victory despite independent observers' reports of widespread irregularities during and after the December vote that have led the main opposition candidates to call for a re-run and allege fraud.
Logistical mishaps, a last-minute extension of voting and a murky tabulation process have stoked ongoing disputes that threaten to further destabilise the poverty-stricken but mineral-rich nation.
Only one opposition presidential contender out of 18, Theodore Ngoyi, took the matter to court after provisional results gave Tshisekedi more than 73% of the vote. One citizen also filed an appeal.
Tshisekedi's main opponents, including runner-up candidate Moise Katumbi, have refused to challenge the vote count in court, citing a lack of trust in state institutions.
The Constitutional Court ruled on Tuesday that irregularities could not have impacted election results because there was such a big gap between Tshisekedi and Katumbi, who won around 18% of votes.
"Even when taking reported irregularities and their influence on the ballot into account, the order of arrival is not disrupted," the court's president, Dieudonne Kamuleta, said.
Tshisekedi's main challengers did not immediately react to the verdict.
The opposition had previously called for the election to be annulled, citing "massive fraud", and urged the international community not to recognize the provisional results.
The government and the electoral commission have said the election was free and fair despite the irregularities and rejected demands for a full re-run.
(Reporting by Ange Kasongo;Writing by Sofia Christensen;Editing by Chris Reese, Bill Berkrot and Emelia Sithole-Matarise)
By Ange Kasongo
