"Having gained. 38.57 percent of the vote, Felix Tshisekedi is provisionally declared the elected president of the Democratic Republic of Congo", said Corneille Nangaa, the head of the Independent National Election Commission (CENI).
"Outgoing President Joseph Kabila will be able to influence Tshisekedi, who now owes his ascendancy to power to Kabila's control of the electoral commission", Robert Besseling, a Johannesburg-based executive director at business risk consultancy Exx Africa, said in an emailed note.
Some observers have suggested President Joseph Kabila's government sought to make a deal as hopes faded for a win for ruling party candidate Emmanuel Ramazani Shadary.
It is not immediately clear whether opposition candidate Martin Fayulu, who led in polling and warned against manipulation, will contest the results.
Runner-up Fayulu dismissed the results, however, claiming that there had been an "electoral coup".
In a conference last week, the Church's bishops said that it knew the identity of the victor and demanded that CENI publish accurate results. "Where did the extra seven million votes come from [for Tshisekedi's victory]?"
The powerful religious institution deployed 40,000 election observers and is considered one of Congo's most influential and trusted institutions.
The announcement came as riot police were deployed in the capital, Kinshasa, amid fears of a disputed result in the December 30 vote marked by accusations of vote fraud.
In order to do so they must appeal to Congo's constitutional court, which has 10 days to hear and rule on any challenges.
"This is the coronation of a lifetime", the deputy secretary-general of Tshisekedi's party, Rubens Mikindo, said shortly after the announcement that his candidate had won, above the cheers at party headquarters.
Tshisekedi, 55, garnered 7.05 million votes, the electoral commission, known as CENI, said in provisional results broadcast on state television Thursday in the capital, Kinshasa. Kabila has promised a peaceful transition of power.
Ahead of the election results, activist groups urged people to "be ready to massively take to the streets" if the outcome didn't match "the truth of the ballot boxes".
The UDPS described Tshisekedi as the presumptive victor with Secretary General Jean-Marc Kabund saying, "the two personalities have an interest in meeting to prepare for a peaceful and civilized transfer of power".
A local observer group said it had witnessed "major" irregularities at counting stations. This is an ugly swindle of [DRC's Electoral Commission President] Mr. Nangaa and his political camp. The Kinshasa lawmaker and businessman said his coalition would release its own figures if the announced results don't conform to the will of the Congolese people.
"Mr. Kabila is a Congolese citizen". About 18.3 million votes were cast, representing turnout of nearly 48 percent.