"Today, at least 171 countries have gathered here in New York to sign the Paris agreement," Ban said. "This is history in the making."
Friday’s event will set a record for the most countries to sign an international agreement on a single day, the secretary general added.
"This is important because it gives a clear symbol that the Paris agreement will be implemented," French President Francois Hollande said during the ceremony.
The deal aims to limit global average temperatures to less than 2 degrees Celsius above pre-industrial levels. The agreement also aims to create more financing for lowering greenhouse gas emissions and support more climate-resilient development.
The United States, China, Russia and EU states are among the countries expected to sign the agreement on Friday. The Russian cabinet endorsed the deal on April 20.