TUNIS—The speaker of Tunisia's parliament was named interim president and talks started on the formation of a caretaker government Saturday, a day after the first successful mass uprising against an Arab leader in years forced former President Zine al-Abidine Ben Ali to flee the country.

Mr. Ben Ali left Friday for Saudi Arabia amid swelling protests against his 23-year autocratic rule. In a statement read on national television Saturday, the head of Tunisia's constitutional council declared the post of the president vacant...