Ministers from both countries signed an agreement brokered by the United Nations and Turkey in Istanbul.
Russia has so far been blocking maritime access to those ports, meaning that millions of tons of Ukrainian grain has not been exported to the many countries that rely on it.
"Today, there is a beacon on the Black Sea. A beacon of hope -- a beacon of possibility -- a beacon of relief -- in a world that needs it more than ever," UN Secretary-General Antonio Guterres said Friday.
"Promoting the welfare of humanity has been the driving force of these talks," he said. "The question has not been what is good for one side or the other. The focus has been on what matters most for the people of our world. And let there be no doubt -- this is an agreement for the world."
Guterres said the deal will bring relief for developing countries and help stabilize global food prices, "which were already at record levels even before the war -- a true nightmare for developing countries."
The World Food Programme (WFP) estimates that 47 million people have moved into a stage of acute hunger as a consequence of the Ukraine war, and Western officials have accused Russia of using food as a weapon during its invasion.
The deal will also allow the unimpeded access of Russian fertilizers to global markets. Russia is a major producer of fertilizers, which are vital to maximizing food production, and the cost of the product has spiralled since the invasion.
Turkish President Recep Tayyip Erdogan said "millions of people will be relieved of this danger of hunger" as a result of the deal.
"In the coming days we will see the start of ship traffic and many countries will have a breath of fresh air," Erdogan said.
How will this deal work?
As part of the deal signed Friday, grain ships would navigate through a safe corridor in the Black Sea under the direction of Ukrainian pilots, and then pass through the Bosphorus strait -- an important shipping corridor in north-west Turkey -- in order to reach global markets.
Vessels would be inspected before they arrive in Ukraine by Russian, Ukrainian and Turkish officials, to ensure weapons are not being smuggled into Ukraine.
The ships will be monitored by a Joint Coordination Centre (JCC) which will be established immediately in Istanbul and include representatives from Ukraine, Russia and Turkey.
Both parties have agreed that there should be no attacks on any of the vessels going from those ports out of territorial waters into the Black Sea by any party.
Before the deal was signed, the Ukrainian government warned Russia against any provocations. "No transport escort by Russian ships and no presence of Russian representatives in our ports," Mykhailo Podolyak, adviser to the Ukrainian president's chief of staff tweeted on Friday.
"In case of provocations, an immediate military response," he added.
Podolyak also added that Ukraine was not signing an agreement with Russia, but with Turkey and the UN. He also said inspections of ships would be carried out in Ukrainian waters, by joint groups, if necessary.
The Black Sea will not be de-mined; a lengthy and complex process that the UN's mining experts, as well as Turkey and Ukraine, agreed was a non-starter. Naval mines in the Black Sea have provided a significant obstacle in efforts to restart grain exports, with Ukraine and Russia accusing each other of mining the waters.
Why are grain exports so important?
Ukraine and Russia are both significant suppliers of food to the world. In normal times, Ukraine -- known as one of the globe's breadbaskets -- would export around three-quarters of the grain it produces. According to data from the European Commission, about 90% of these exports were shipped by sea, from Ukraine's Black Sea ports.
The war and its impact on grain exports therefore has major implications, particularly in the global South which relies heavily on them. Between disrupting Ukrainian agricultural production and blocking the export of products that remain, Russia's war in Ukraine could push 49 million people into famine or famine-like conditions, the United Nations warned last month.
This year's harvest is underway in Ukraine, adding further urgency to negotiations. Fields have come under attack in recent days,
leaving farmers racing to save their crops. Storage issues have also hampered farmers; last month, a grain storage silo was destroyed in the city of Mykolaiv, which Ukraine says Russia hit with air-based cruise missiles.
The UN is hoping that under the deal, a monthly export of 5 million tons of grain would leave the ports each month, a figure comparable to pre-war levels.
How has the war impacted Ukraine's harvests?
While the ability to export grain to the Black Sea is a major breakthrough, the amount Ukraine can ship has been severely affected by war.
The President of the Ukrainian Grain Association, Mykola Horbachov, said on Friday that unblocking Ukrainian ports is the only way to prevent a global food crisis and save Ukrainian agricultural producers. He said the Russians had stolen about 500,000 tons of grain in occupied territories, and approximately 1 million tons of grain remains in the elevators under the control of the occupiers.
Earlier this month, Ukraine's grain traders' union said it expected a grain and oilseed
harvest of 69.4 million tons, marginally higher than previous forecasts but far below the 106 million tons harvested last year.
Deputy Agriculture Minister Taras Vysotskiy said the grain harvest could be at least 50 million tons, compared to 86 million tons in 2021. At least half that output is earmarked for export, according to the traders' union.
The production and export of wheat in an already tight global market may be most at risk. French consultancy Agritel said this month it expects Ukraine to harvest 21.8 million tons of wheat this summer compared to 32.2 million last year.
Ukraine's Infrastructure Minister, Oleksandr Kubrakov, described the deal that he signed at the Istanbul ceremony as "a great support for the Ukrainian economy."
Will Russia stick to the deal?
Western officials have accused Russia of deliberately strangling the global supply chain during the country's war in Ukraine. European Commission Chief Ursula von der Leyen has said that food was part of the Kremlin's "arsenal of terror," and the US accused it of having "weaponized" food.
The US and other Western nations have hailed Friday's agreement. But US State Department spokesman Ned Price cautioned on Thursday, when an agreement was reached in principle, that Washington would focus on "holding Russia accountable for implementing this agreement."
British Foreign Secretary Liz Truss said Friday: "The UK and our allies have been pushing hard to reach this point. Now this agreement must be implemented, and we will be watching to ensure Russia's actions match its words."
Correction: A previous version of this story misstated Taras Vysotskiy's position in the Ukrainian government. He is deputy agriculture minister.
