During the address at 9 p.m. EDT from Fort Myer, Va., Trump will "provide an update on the path forward for America's engagement in Afghanistan and South Asia," the White House said in a statement Sunday. Fort Myer is a U.S. Army post next to Arlington National Cemetery in Arlington County and across the Potomac River from Washington, D.C
"The president has made a decision," Mattis told reporters on an overnight flight that arrived in Amman, Jordan, on Sunday. "I am very comfortable that the strategic process was sufficiently rigorous."
On Friday, Trump met with top administration officials, including Mattis, Secretary of State Rex Tillerson, National Security Adviser H.R. McMaster and Vice President Mike Pence at Camp David in Maryland.
Trump, who returned to his golf course in Bedminister, N.J., later that day, posted Saturday on Twitter: "Important day spent at Camp David with our very talented generals and military leaders. Many decisions made, including on Afghanistan."
Trump press secretary Sarah Huckabee Sanders said Friday a new strategy would "protect America's interests" in the South Asian region and details would be forthcoming.
Mattis told reporters, "It is a South Asia strategy; not just an Afghanistan strategy," indicating it will also include Pakistan and India.
In June, Mattis was given authority to send nearly 4,000 troops to Afghanistan to advise and support Afghan forces. Mattis held off expanding the American forces.
Other options include withdrawing them altogether, leaving private military contractors to help manage security.
An estimated 9,800 American troops are in Afghanistan, mostly assigned to an international force of about 13,000 assisting the Afghan military.
In February, Gen. John Nicholson, the commander of the American-led international force in Afghanistan, told Congress that the United States and its NATO allies were facing a "stalemate."
Mattis met with Jordan's King Abdullah, as well as top Jordanian defense officials, and is scheduled to go Wednesday to Turkey where he will meet with President Recep Tayyip Erdogan and other leaders.
"Secretary Mattis will emphasize the steadfast commitment of the United States to Turkey as a NATO ally and strategic partner, seek to collaborate on efforts to advance regional stability, and look for ways to help Turkey address its legitimate security concerns -- including the fight against the PKK," the Pentagon said in a statement Friday.
The PKK, also known as the Kurdistan Workers' Party, is listed as a terrorist group by the United States and many European nations, and has been leading an insurgency against the Turkish government since 1984.
Mattis plans to meet with Ukrainian Defense Minister Stepan Poltorak and President Petro Poroshenko in Kiev Thursday. The Trump administration is considering providing lethal defensive weapons to Ukraine to fight Russian-backed separatists.
"During these engagements, the secretary will reassure our Ukrainian partners that the U.S. remains firmly committed to the goal of restoring Ukraine's sovereignty and territorial integrity," the Pentagon statement said.