The US leader will "provide an update on the path forward for America's engagement in Afghanistan and South Asia" in an address to be delivered at 9 pm (0100 GMT Tuesday) from the military base at Fort Myer southwest of the capital, the White House said in a statement.
Trump gathered top security officials Friday at the Camp David presidential retreat in Maryland to weigh his options in the grueling conflict, saying afterwards that "many decisions" had been made.
Wary of international involvements but eager for progress in the drawn-out Afghan war, the Trump administration had originally promised a new plan by mid-July.
Trump was said to be dissatisfied by initial proposals to add a few thousand more troops in the country, and advisers were studying an expanded strategy for the broader South Asian region, including Pakistan.
The decision comes after the departure from the White House on Friday of Steve Bannon, Trump's firebrand chief strategist, a nationalist who was said to be disinclined to seeing US forces more deeply mired in the troubled region.
Trump's Defense Secretary Jim Mattis confirmed in Amman, Jordan on Sunday that the administration had agreed on a new strategy for Afghanistan after "rigorous" debate, but refused to provide any details about the decision.
"Everyone who had equity was heard," he said, including budget officials responsible for funding the effort.
Trump had several options on the table, that ranged from backing away from the country to stepping up US efforts to defeat the Taliban. In June he gave Mattis the power to increase troop numbers above the estimated 8,400 that have been in the country -- close to 4,000 more, according to reports.
Mattis arrived in Jordan Sunday on the first day of a five-day swing through the Middle East, Turkey and Eastern Europe.
There are now about 8,400 US and 5,000 NATO troops supporting Afghanistan's security forces in the fight against Taliban and other militants. But the situation has remained as deadly as ever, with more than 2,500 Afghan police and troops killed from January 1 to May 8.
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