"This will send a strong political message of NATO's commitment to the fight against terrorism," Stoltenberg said.
He stressed this did not involve NATO taking on a combat role in the fight against ISIS and other Islamist terror groups in Syria and Iraq.
Trump came to Brussels on his first foreign trip as president to push NATO allies to take on a more active role, having dubbed the Cold War-era alliance "obsolete" for failing to focus on the threat from Islamist terrorism.
Arriving in the city Wednesday, Trump said Monday's deadly bomb attack in Manchester only showed how dangerous the threat was and that the fight against terror had to be won.
All 28 allies have individually joined the anti-ISIS coalition of more than 60 countries, but NATO as an institution has not followed suit until now despite intense pressure from Washington.
Diplomatic sources say some member states such as France, Germany and Italy had opposed such a move for fear the alliance would be dragged into a ground war and risk relations with Arab powers.
Stoltenberg said NATO would expand the role of its AWACS surveillance planes in supporting anti-ISIS operations and step up its training programmes in Iraq.
A special cell would be set up at NATO headquarters in Brussels to coordinate anti-terror intelligence and planning, he said.
He said the allies would also meet Tusk's demands to share more of the security burden and reaffirm a commitment to spend two percent of annual GDP on defence.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)