Moldovan authorities have released Renato Usatii, the leader of the pro-Moscow Our Party, from custody.
A court in Chisinau rejected the prosecutors' request to extend Usatii's detention by 30 days and ordered that he be freed.
"Thank you very much." Usatii told hundreds of his supporters outside the courtroom. "We'll continue the struggle against corrupt authorities."
Usatii, who is the mayor of Moldova's second-largest city, Balti, was detained on October 23 at Chisinau airport on suspicion of violating privacy laws.
Usatii had published a telephone conversation on his Facebook page between a businessman and former Prime Minister Vlad Filat, who was arrested this week and charged with taking a $260 million bribe.
Usatii's party was banned from taking part in the November 2014 parliamentary election because it received money from abroad.
Its leader fled Moldova, saying he feared arrest, but later returned to run for mayor of Balti.