- Tag results for Zimbabwe Election
Chamisa, who heads the Movement for Democratic Change (MDC), narrowly lost to Emmerson Mnangagwa in Zimbabwe's first election since the ousting of long-time ruler Robert Mugabe last year.
In his first comments since the country's top court overturned the opposition's legal challenge to have the results annulled, Chamisa vowed to lead "peaceful protests".
The Movement for Democratic Change accused ruling ZANU-PF party and election commission of rigging July 30 vote, Zimbabwe's first poll since the ousting of Robert Mugabe.
The comments are in sharp contrast with President Emmerson Mnangagwa's previous efforts to woo Western governments.
Nelson Chamisa won 44.3 percent in the historic first election following the ousting of autocrat Robert Mugabe, according to the Zimbabwe Election Commission.
Zimbabwe's closely-watched elections began with Monday's peaceful vote but turned deadly 48 hours later when the military fired on protesters and six people were killed.
Zimbabwe opposition urge transparency in results, accuses President Emmerson Mnangagwa of vote-rigging
The opposition said it will challenge in court the results of the election, which Mnangagwa won with just over 50 per cent of the vote.
The Zimbabwe Electoral Commission (ZEC) announced that Mnangagwa, 75, received 2,460,463 votes, representing 50.8 per cent of the total votes, reports Xinhua news agency.
While the Zimbabwe Electoral Commission (ZEC) insists the election was fair, the opposition Movement for Democratic Change (MDC) has raised an array of fraud allegations.
Zimbabwe on Thursday awaited the outcome of presidential elections that have plunged the country into bloodshed and protest, stirring memories of a traumatic past.
The man died after soldiers fired live ammunition during opposition protests in downtown Harare, AFP reporters saw.
The EU mission found an "improved political climate, but (an) un-level playing field and lack of trust in the process," it said in a statement.
If required, Zimbabwe's 5.6 million registered voters would be asked to return to the polls to vote in a presidential run-off on September 8.
About 5.5 million people were registered to vote in this southern African nation anxious for change after economic and political paralysis during the nearly four-decade rule of the 94-year-old Mugabe.
In the country's first election since Mugabe was ousted after 37 years in power, Zimbabwe goes to the polls Monday amid mounting allegations of voter fraud and predictions of a disputed result.