Russian artist Pyotr Pavlensky was put under formal investigation on Tuesday after the publication of an online sexual chat that caused one of French President Emmanuel Macron's closest lieutenants to pull out of the race to become mayor of Paris.
The Paris prosecutor's office said Pavlensky had been released from a police station on Tuesday evening after having been brought in for questioning on Sunday.
Pavlensky, who has lived in France since 2017, faces charges of privacy violation.
His girlfriend was also placed under formal investigation, the prosecutor's office said, adding they were not permitted to contact each other.
Benjamin Griveaux, 42, a key member of Emmanuel Macron's LREM party, said last week he had decided to withdraw from the municipal election next month.
Pavlensky had claimed he had published screenshots of an online chat which he said was between Griveaux and a woman who is not his wife.
The chat included a video showing a man's genitals. Griveaux has not disputed that he sent the messages.
In France, a formal investigation may or may not lead to a trial.
Macron has since picked health minister, Agnes Buzyn, to revive his efforts to win control of the Paris city hall.
French politicians from all sides denounced the leak of private material, which many said constituted an unacceptable Americanization of politics in France, where politicians' private lives have long been considered off-limits.
Pavlensky is best known for works of performance art including nailing his scrotum to the ground in Moscow's Red Square and setting fire to doors at the headquarters of Russia's state security agency and the Bank of France.
