Salvador Nasralla conceded shortly after Honduras' key ally Washington endorsed President Juan Orlando Hernandez's re-election, following a month of sometimes deadly street clashes.
Honduran opposition candidate Salvador Nasralla said his bid for the presidency was a "lost cause" on Friday after the United States recognised President Juan Orlando Hernandez as winner of the election.
"The situation is practically decided," Nasralla said in an interview with TV network France 24. "I no longer have anything to do in politics, but the people, which are 80 percent in my favour, will continue the fight."
The Honduran electoral tribunal declared Hernandez winner of the November 26 election last weekend amid strident opposition protests over the vote count in the impoverished Central American country.
The controversial election came eight years after a military coup sparked by a previous president's flirtation with a second term, which was barred by the constitution at the time. In that case, the turmoil was sparked by leftist leader Manuel Zelaya.
The vote tally had initially clearly favoured opposition candidate Salvador Nasralla, a centre-leftist, but it swung in favour of the incumbent after a 36-hour delay.
The final result sparked violent protests in Honduras, and the Organization of American States (OAS) has called for new elections to resolve the dispute.
That proposal was rejected by senior Honduran officials before the US government recognized Hernandez as president.
"We congratulate President Juan Orlando Hernandez on his victory in the November 26 presidential elections, as declared by the Honduran Supreme Electoral Tribunal," US State Department spokeswoman Heather Nauert said in a statement.
Nauert said Honduras should pursue a "long-term effort to heal the political divide in the country and enact much-needed electoral reforms."