Bulgaria's switch from the lev to the euro comes nearly 19 years after the country of 6.4 million people joined the European Union.
"We did it!" Bulgarian Prime Minister Rossen Jeliazkov said.
"We thank all institutions, partners and everyone whose efforts made this landmark moment possible. The government remains committed to a smooth and effective transition to the euro in the interest of all citizens," Jeliazkov said on X.
In adopting the legal texts necessary for the move, EU finance ministers officially set the euro at 1.95583 Bulgarian lev.
EU chief Ursula von der Leyen and European Central Bank head Christine Lagarde congratulated Bulgaria after the ministers' approval.
"We are delighted to welcome you," Lagarde said.
"The euro will strengthen Bulgaria's economy and bring big benefits for Bulgarian people and businesses," von der Leyen said on X.
"Joining the euro area is much more than just about replacing lev with euro. It is about building a brighter and more prosperous future for Bulgaria and its citizens at the heart of Europe," EU economy chief Valdis Dombrovskis said.
The European Commission last month said the EU's poorest country had fulfilled the strict conditions to adopt the euro, while the ECB also gave a positive opinion.