The 44-year-old still has to be sworn in by King Philippe, who is expected to announce the nomination formally on Sunday at the earliest.
Michel, who is set to take over as European Council president on December 1, had said on Friday he intended to step down by the beginning of November "at the latest".
Belgium has not had a fully functioning federal government since a coalition headed up by Michel collapsed in December 2018.
He has stayed on as caretaker premier ever since.
The political situation was further complicated by a very fragmented result of parliamentary elections in May.
"Congratulations Sophie Wilmes, who is being put forward to the King as caretaker prime minister," Michel said on Twitter.
Félicitations @Sophie_Wilmes qui sera proposée au Roi comme Première Ministre en affaires courantes.
— Charles Michel (@CharlesMichel) October 26, 2019
Hartelijke gelukwensen aan @Sophie_Wilmes de eerste vrouw als toekomstige eerste minister in lopende zaken.
Wilmes, who is seen as an ally of Michel's and was first elected to parliament in 2014, was chosen by a ministerial committee.
Belgium has a reputation for political crises. In 2010-2011 it was without a government for 541 days - a record.
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