Born in Bistrița, Hartig studied at the Gheorghe Dima Music Academy in Cluj-Napoca, graduating in 2006.

Hartig has had particular success in the role of Mimì in Puccini's La bohème. She first sang Mimì in 2006 at the Cluj-Napoca Romanian National Opera. She sang the role in Welsh National Opera's 2012 new production directed by Annabel Arden, and has since sung the role with The Royal Opera, London, the Metropolitan Opera, New York, and the Vienna State Opera. In 2012, London's Daily Telegraph reported that she was "enjoying special success" as Mimì.