The victory on Saturday came in Baghouz, the remote riverside village where Takfiri militants of a variety of nationalities made a desperate, dramatic last stand.
"Syrian Democratic Forces declare total elimination of so-called caliphate and 100 percent territorial defeat of ISIS," spokesman Mustefa Bali said in a statement, using another acronym for Daesh.
The recapture of the territory now removes the last hurdle to its return to the Syrian government fold even though the US military presence remains yet another sticking point.
The US professes support for Syrian Kurds, including Syrian Democratic Forces, but many observers see it in the context of Washington's plans to carve out a foothold in the region.
US leaders have always tried to hijack major victories achieved in Syria. On Friday, US President Donald Trump said Daesh no longer held any territory in Syria.
The United States is also a key advocate of autonomy for Syrian Kurds which Damascus has roundly rejected.
Last month, a senior adviser to Syrian President Bashar al-Assad flatly rejected the idea of giving Syrian Kurds a measure of autonomy, saying such a move would open the door to the partition of the country.
The Kurdish-led authority that runs much of north and east Syria has presented a roadmap for a deal with Assad in recent meetings with Russia.
The Kurds want to safeguard their region inside a Syrian state when US troops pull out and hope a deal with Damascus would dissuade neighboring Turkey from attacking them.
Syrian Deputy Foreign Minister Faisal Mekdad has expressed optimism over dialogue with Kurdish groups as he stressed that Damascus wanted to retake every inch of territory lost during eight years of war.
“Autonomy means the partition of Syria. We have no way to partition Syria,” senior adviser Bouthaina Shaaban said last month.
“Syria is a country that is a melting pot for all people and all people are equal in front of Syrian law and in front of the Syrian constitution,” she added, calling the Kurds “a precious and very important part of the Syrian people.”
She also criticized Turkish President Tayyip Erdogan and his idea of carving out “a safe zone” in northeast Syria.
“Turkey has all the new ambition to occupy other people’s land and I think we are facing Erdogan who has dreams of reinvigorating and recreating the Ottoman Empire,” she said.
“But I don’t think he will be able to do that because our people are there to defend our land.”
Last month, Syrian President Bashar al-Assad called on SDF militants to return to the Syrian army, warning them against reliance on the United States.
“We say to those groups who are betting on the Americans, the Americans will not protect you. The Americans will put you in their pockets so you can be tools in the barter, and they have started with it," he said.
"Nobody will protect you except your state. If you do not prepare yourselves to defend your country, you will be nothing but slaves,” Assad added.
In December, the US president said he would withdraw all 2,000 troops from Syria. However, the Wall Street Journal said recently that Washington planned to keep about 1,000 troops in Syria.
US Joint Chiefs Chairman General Joseph Dunford later rejected the report as “factually incorrect,” stressing that there was no change to the planned 400 troops which the White House wanted to keep in Syria.
Trump’s December announcement to withdraw all troops from Syria has infuriated the UAE crown prince, according to a recent report by Middle East Eye.
“You are leaving Syria to be under Iranian and Turkish influence and that will bring everyone back. They will act against your acts and our interests,” Mohammed bin Zayed told US Secretary of State Mike Pompeo.
The crown prince said if the US changed its mind, the United Arab Emirates would be prepared to fund the cost of keeping US troops in Syria from its own budget, the report added.