Baltic leaders withdrew their first euros from a Vilnius bank machine just after midnight, as the eurozone gained its 19th member and fireworks signed off a year marked by alarm over Russia's role in the Ukraine conflict and its economic crisis.
For a nation scarred by decades of Soviet occupation, eurozone entry is an important step and a symbol of "deeper economic and political integration with the West", Lithuanian President Dalia Grybauskaite said.
A total of 337 million Europeans now share the euro currency.
The three Baltic states broke free from the Soviet Union in 1990-1991 before joining the EU and NATO in 2004. Estonia and Latvia became eurozone members in 2011 and 2014.
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"In joining the euro, the Lithuanian people are choosing to be part of an area of stability, security and prosperity," EU economic affairs commissioner Pierre Moscovici said.
Fifty-three per cent of the population of three million backed the euro and 39 per cent were against, according to a November survey released by the central bank.
"I support the euro because it leads to greater integration into the EU and makes travelling in the EU easier," said 26-year-old lawyer Karolis Turcinavicius.
But pensioner Danute Petkeviciene remained skeptical: "The euro will not increase pensions or wages, it will only increase prices."
Vilnius resident Teresa said she regretted losing a symbol of the country's statehood.
Lithuania's membership comes as political uncertainty in Greece is once again stoking fears that the eurozone's debt crisis could flare up.