The tech giant said there would be a "one-strike policy" banning those who violate new Facebook Live rules.
New Zealand Prime Minister Jacinda Ardern called the measures a "good first step".
In March the gunman live-streamed the attacks in New Zealand, where 51 people died.
Ms Ardern is chairing the summit with French President Emmanuel Macron. It aims to co-ordinate international efforts to stop social media being used to organise and promote terrorism.