The protesters are demanding a non-elected people's council lead the country instead.
Thailand has been plagued by political turmoil since Yingluck's brother Thaksin Shinawatra, a former premier, was toppled in a 2006 military coup.
In broad terms, the confrontation pits the Thai elite and the educated middle-class against Thaksin's power base in the countryside, which benefited from populist policies designed to win over the rural poor.
At least five people have been killed and at least 289 injured since the latest unrest began.
Several days of violence ended suddenly last week as both sides paused to celebrate the birthday of the nation's revered king, who turned 86 Thursday.
But protesters have vowed a final showdown Monday in Bangkok and will march en masse from a government complex they seized to Yingluck's office.
Democrat leader and former premier Abhisit Vejjajiva told reporters the resignations were effective immediately.
He said Yingluck's government has been “illegitimate” ever since her ruling party tried to ram through an amnesty bill that critics allege was mainly designed to bring back Thaksin from exile.
Thaksin lives in Dubai to avoid a jail sentence for a corruption conviction he says was politically motivated.
Updated on: December 08, 2013 18:57 IST
