The move comes after the country's highest court ordered authorities to restore access, saying the ban violated laws on freedom of expression.
The ban was imposed in late March, soon after recordings alleging official corruption were aired on the site.
Turkey passed a controversial law early this year that let regulators cut off any site without needing a court order.
Authorities had continued to block YouTube until now despite decisions from lower courts calling on the government to lift the ban.
The ruling by the constitutional court is widely seen as a snub to the government of Prime Minister Recep Tayyip Erdogan, which has been a sharp critic of social media sites.
Both YouTube and Twitter were blocked after recordings of official meetings were leaked and widely circulated.
One recording involved senior army officers discussing intervention in Syria and others supposedly revealed corruption among people close to Mr Erdogan.
The block was imposed as a "precautionary administrative measure", Turkey's telecommunications regulator had said at the time.
YouTube was blocked previously in Turkey in 2007 but that ban was lifted in 2010.