Prime Minister Boiko Borisov, a former bodyguard who swept to power in 2009 on pledges to root out corruption and raise living standards in the European Union's poorest member, now faces a tough task to prop up eroding support ahead of a probable early election.
Wage and pension freezes and tax hikes have bitten deep in a country where living standards are less than half the EU average and tens of thousands of Bulgarians have rallied in protests that have turned violent, chanting "mafia" and "resign".
On Tuesday, 11 people were taken to hospital – including one man bleeding heavily from the head – and 11 arrested after protesters threw flares at police, who fought demonstrators with shields and truncheons.
Announcing his resignation yesterday, Mr Borisov said: "I will not participate in a government under which police are beating people."
He began his career guarding the Black Sea state's communist dictator Todor Zhivkov.
Parliament was expected to accept the resignation.
The spark for the protests was high electricity bills, after the government raised prices by 13% last July. But it quickly spilled over into wider frustration with Mr Borisov's domineering manner and unpredictable decision making.
The Prime Minister made sacrifices in an attempt to cling on, sacking his finance minister, cutting power prices and risking a diplomatic row with the Czech Republic by punishing foreign-owned companies, a move that conflicted with EU norms.
His rightist GERB party is the dominant faction in parliament but will not take part in talks to form a new government, Interior Minister Tsvetan Tsvetanov said, indicating elections would be brought forward.