Skopje and Athens buried a 27-year dispute in agreeing in June last year to rename Macedonia as North Macedonia.
The new name came into force on Tuesday after constitutional changes were published in the Official Gazette and Skopje’s foreign ministry said both countries had informed the UN by letter that the change is now in force.
Skopje is already using the new full name — Republic of North Macedonia — on its official website and Twitter page while the authorities were due later Wednesday to change border signs.
Since 1991, Athens had objected to its neighbour being called Macedonia because Greece has a northern province of the same name.
The issue has held up Macedonia’s attempts to join NATO and the European Union.
Overcoming opposition of hardline nationalists in both countries, Macedonian Prime Minister Zoran Zaev and Greek counterpart Alexis Tsipras managed to strike a deal which both parliaments ratified last month.