The opposition Union of Democratic Forces (UDF) elected Boris Markov as acting chairman until July 8 when the party will vote for a leader.
Markov's nomination was backed by 53 party members, one voted against and 15 abstained, UDF said in a press release on its website on Tuesday.
Markov succeeds Martin Dimitrov who resigned last month after the UDF decided against running in the forthcoming general elections in a coalition with its traditional partner, the Democrats for Strong Bulgaria.