During President Biden’s administration, Rachel Maddow scaled back her broadcast schedule, reducing her popular prime-time show on MSNBC to once a week.

With the return of President-elect Donald J. Trump to power, she will return to full-time service.

MSNBC said Monday that Ms. Maddow would temporarily return to airing her hour-long show every week at 9 p.m. Eastern time for the duration of Mr. Trump’s first 100 days in office.

Through April 30, Alex Wagner, the anchor who occupied Ms. Maddow’s Tuesday-Friday time slot, will instead file reports from around the country “on the impact of Trump’s early policies and promises on the electorate,” the network said.

Ms. Maddow signed a lucrative contract in 2021 that significantly increased her compensation while reducing her on-air commitments. Since then, she has produced several podcasts and documentaries, although MSNBC viewers regularly saw her hosting major events such as election night and political conventions last summer.

After April 30, Ms. Maddow will host only on Mondays, with Ms. Wagner taking over the rest of the week.

MSNBC’s ratings plummeted after Mr. Trump’s re-election in November. Network executives hope audiences will return as Mr. Trump takes office and viewers try to analyze his early political moves. Other changes include a new fact-checking segment called “Here Is What Is True,” hosted by Chris Hayes.

Fox News also announced a programming change on Monday. Will Cain, a conservative pundit and weekend host of “Fox & Friends,” will leave his morning role and take over the network’s weekday 4 p.m. hour. That slot was previously occupied by a straightforward news show hosted by Neil Cavuto, a veteran business journalist who signed off from the show in December.