Tunisian media reported that Gharsalloui previously headed several departments of the president's security service.
"President #Kais_Saied issues a presidential decree designating Ridha Gharsalloui as acting Interior Minister," the presidency tweeted.
According to the president's office, Gharsalloui has already taken the oath as the interim head of the ministry.
The appointment came following mass anti-government protests that erupted in the country's capital of Tunis past Sunday. Saied had dismissed Prime Minister Hichem Mechichi, suspended the parliament for 30 days and frozen the legal immunity of lawmakers. The president has temporarily fully assumed executive power, saying that he would appoint a new prime minister soon.
On Monday, Ennahda, the largest political party in the Tunisian parliament, labeled Saied's move unconstitutional and equal to a coup.
The Tunisian constitution provides for a sharing of executive power between president, prime minister and parliament. The president and the parliament were elected in separate votes in 2019, while the prime minister took his office last summer. Since then there have been political disputes between Saied and Mechichi, with COVID-19 exacerbating the wrangling.