Sebe ran the company since 2005, and she will now be in charge with worldwide development and production operations, Avangate said in a news release.
Theobald has more than 20 years experience in the software industry, taking management positions in large companies as well as start-ups, including Oracle, RubiconSoft and Serena Software.
Theobald is also a member of the Avangate board.
Avangate was detached from e-commerce firm GECAD ePayment and it is owned by local entrepreneur Radu Georgescu, through Cyprus-registered Orbitview. Private equity firm 3TS Capital Partners owns a minority stake in Avangate.