The former Chelsea man, who was sacked by the Stamford Bridge club in 2004 after failing a drugs test, will leave current employers Ajaccio on a loan deal.
Mutu announced the move on Twitter, writing: "From January I will play for Petrolul Ploiesti. I will come on a loan from Ajaccio."
Petrolul Ploiesti were knocked out of this season's Europa League by Swansea City, who won 6-3 on aggregate.
Mutu has not played club football in Romania since 2000 when he left Dinamo Bucharest.
The 34-year-old is currently banned from international football after mocking national team coach Victor Piturca, whom he likened to Mr Bean.