Stoltenberg was to participate in a Kabul media conference later Saturday with Afghan President Ashraf Ghani and US Defense Secretary Mark Esper, the NATO statement said, AFP reported.
He was also to meet the head of the US and NATO forces in the country, General Scott Miller, as well as other commanders of the alliance's training mission there.
The details of the deal, to be signed in Doha on Saturday, have not been disclosed, but it is expected to set the terms of the US to start withdrawing the more than 12,000 troops it has in Afghanistan in return for commitments from the Taliban.
It carries with it hopes of a fall in violence in Afghanistan after decades of conflict and the opening of peace talks with the Afghan government, which was excluded from the direct US-Taliban negotiations.