The premier of the western German state of Rhineland-Palatinate, Malu Dreyer, announced her resignation on Wednesday.
Dreyer, a Social Democrat who has led the state since 2013, said she would leave the post in July.
The reason for her decision was not immediately clear, although there had been considerable speculation about her possible retirement. Her office said she would address her resignation at a 2pm (1200GMT) news conference.
Dreyer's resignation comes less than two weeks after her Social Democratic Party (SPD) suffered a major defeat in European Parliament elections, and also lost ground in local elections held in the state.
Sources told dpa that she would be replaced by Alexander Schweitzer, another Social Democrat. He currently serves as the state's minister for labour and social affairs.
That would give the 50-year-old Schweitzer the opportunity to head into the next state parliamentary election - scheduled for 2026 - as an incumbent.
Political scientist Uwe Jun acknowledged on Wednesday that Dreyer had chosen a good time to step down with less than two years before the next state election.
Jun told dpa that her successor will have enough time to take office and make his mark, although Jun said that Schweitzer has "very big shoes to fill" given Dreyer's long tenure and very high popularity ratings among voters in the state.
The main challenger for the post in 2026 is expected to be Gordon Schnieder of the centre-right Christian Democrats (CDU).
The SPD has held power in the state since 1991, but appeared to lose ground in the recent voting. Sources in both the SPD and CDU had said that state party leaders planned to begin preparations for the 2026 vote after the EU elections.
Sources told dpa that two other Social Democrats - state Interior Minister Michael Ebling and state parliamentary group leader Sabine Bätzing-Lichtenthäler - had also been considered as possible successors to Dreyer.
On Wednesday, dpa also learned that long-time state SPD party chairman for Rhineland-Palitanate, Roger Lewentz, also plans to resign and will be replaced by Bätzing-Lichtenthäler.
