It will be the first meeting of its kind since Nigeria's election a week ago which was won by Muhammadu Buhari, a former military leader who has vowed to rid his country of the "terror" of Boko Haram.
A regional coalition involving troops from Nigeria, Chad, Niger and Cameroon has been waging offensives against the Islamists in a bid to crush the insurgency, which has now spread across borders from Boko Haram's stronghold in Nigeria.
"In the face of the mounting and increasingly bloody attacks by the fundamentalists against Nigeria, Niger, Cameroon and Chad and the series consequences for these countries, and the real risk of destabilising western and central Africa, the two organisations have decided to take action," the ECOWAS statement said.
It was not immediately clear if Buhari would be attending as he will not be sworn in as president to succeed incumbent Goodluck Jonathan until May 29.