The deal, which representatives from all parties have just signed in Istanbul, means Russia agrees to a truce to allow grain exports.
It’s considered a diplomatic victory in the war, which is now entering its sixth month.
But Guterres added the deal “did not come easy… it has been a long road”.
Saying the deal will benefit developing countries “on the edge of bankruptcy and the most vulnerable people on the edge of famine”.
Russian and Ukrainian representatives declined to sit at the same table at the ceremony, and the display of the two countries’ flags was adjusted so that they were no longer next to one another.
The representatives signed mirror documents, each agreeing to deal with the UN and Turkey but not each other.
Turkish President Recep Tayyip Erdogan welcomed attendees to Istanbul, saying : “We are proud to be instrumental in an initiative that will play a major role in solving global food crisis that has been on the agenda for a long time,” he says.
Turkey will inspect ships to ensure they are not carrying weapons.