Belgium's King Philippe officially named Budget Minister Sophie Wilmes as interim prime minister, making her the first woman to hold the post.
Ms Wilmes, a liberal francophone, replaces Charles Michel, who is set to take over as European Council president in December.
She made her political debut in 2000 as a councillor in Uccle, outside Brussels.
She went on to become a member of parliament in 2014 and joined the federal government a year later.
Ms Wilmes was selected as the caretaker prime minister by a small ministerial committee, but she has no parliamentary majority.
Belgium has not had a fully functioning federal government since a coalition headed up by Michel collapsed in December 2018.
Negotiations to form a new coalition have stalled since parliamentary elections in May produced fragmentary results.
Since early October, talks between the French-speaking socialist PS party and the Flemish nationalist N-VA party to form a new government have collapsed.
The parties must first bridge their differences before they can form a government and bring in other parties.
The first report on their negotiations must be submitted to King Philippe on 4 November.
Belgium, which hosts NATO and the EU, has a reputation for being ungovernable.
In 2010-11, it had a record 541 days without a government.