Disturbances carried on after nightfall in Athens but events on the street failed to prevent what demonstrators had dreaded.
Debt-ridden Greece has now given final approval to more austerity measures, cutting wages and raising taxes. All but one of the ruling Socialist MPs in parliament voted for every provision in the belt-tightening law, needed to secure fresh international bailout funds.
The rebel deputy has now been expelled from the party.
In a second day of protests, tens of thousands of Greeks gathered to oppose the move. But clashes broke out between rival groups and then with the police. One man died of a heart attack but officials said he was not hurt in the incidents.
The violence overshadowed day two of a 48-hour strike against the austerity measures that brought much of Greece to a standstill.