Bettsy Chávez was ousted as culture minister when former prime minister Aníbal Torres resigned on Thursday.
Torres is the longest-serving prime minister, nine months, since Castillo came to power in July 2021.
The one with the shortest time in office is Torres' representative Héctor Valer Pinto who was prime minister for only one week at the beginning of February.
Since last July, President Castillo has faced two impeachment attempts in parliament and is under investigation in six corruption cases.
Castillo immune until 2026
Earlier in November, thousands of people marched in the capital demanding the ouster of the former teacher from the countryside, who unexpectedly seized power from Peru's traditional political elite.
Castillo has denounced the corruption charges as politically motivated and enjoys immunity until the end of his term in July 2026.
Chávez, the left-wing politician, now has 30 days to be approved by parliament in order to assume the prime ministership.