Avelino Guillen, a former prosecutor, is known for prosecuting former President Alberto Fujimori, who is serving a 25-year prison sentence for corruption and human rights violations.
Guillen, 67, will take over from Luis Barranzuela, who resigned as interior minister on Tuesday after hosting a party on Halloween despite a ban on social gatherings amid the COVID-19 pandemic.
Peru: Interior Minister Resigns Amid 'Halloween Party' Scandal
Peru’s opposition-controlled Congress is expected to decide later on Thursday whether to confirm Castillo’s new cabinet, after his first was dissolved last month.
Castillo, a leftist former teacher’s union leader who took office in July after a hard-fought election victory, has had a difficult start to his presidency, given that last month, he swore in a new prime minister, Mirtha Vasquez, after her predecessor resigned.
The government cabinet fell apart amid threats from the right after ex-Prime Minister Guido Bellido proposed nationalizing the country’s natural gas sector.
Under Peruvian law, the prime minister’s resignation automatically triggers that of the entire cabinet.
Castillo also made other changes to his government after facing criticism about his foreign minister denouncing that the Shining Path - a Maoist rebel group that an official Truth and Reconciliation report said was responsible for killing at least 28,000 people in Peru between 1980 and 200 - was a construct of the CIA.
It is still unclear whether Congress will approve Castillo’s new cabinet.
His struggles with Congress are also partially because Castillo has sought distance from his Peru Libre party, with some members announcing they will reject his new cabinet.
The Peru Libre party holds 37 seats out of the 130-member Congress.
Keiko Fujimori, the leader of the political movement first created by her father Alberto, has also stated her party, which holds 24 congressional seats, will vote against the confirmation.
Fujimori, facing corruption charges, lost the presidential election to Castillo by 44,000 votes.