The size and mood of the rally, the first big protest in almost a month, will signal just how bitterly a restive public will fight further tax rises and spending cuts that international lenders demand in return for a massive bailout.
"Many people don't expect any solution, but others hope too much. Deep inside, everyone knows policies cannot change and the measures may be even worse," said Mary Bossis, professor of International Security at the University of Piraeus.
Polls show three quarters of Greeks back former European Central Bank vice president Papademos, a non-party technocrat, after decades of rule by the Socialist PASOK party and conservative New Democracy -- together blamed for leading Greece to the brink of bankruptcy.
Papademos's crisis coalition, which includes those parties, cleared its first hurdle Wednesday by overwhelmingly winning a vote of confidence.
It now faces the much sterner task of keeping the fractious coalition parties behind unpopular reforms.
That job begins Friday when the government submits to parliament a budget of tax hikes and spending cuts that international lenders from the European Union and International Monetary Fund have insisted upon before unblocking an 8 billion euro ($10.8 billion) tranche of financial aid.
Thursday's rally commemorates Greece's bloody 1973 student uprising that helped topple its military junta and will remind members of parliament that after four years of recession, tax rises and cuts to pensions and wages, Greeks are fed up.
"This government will do better (than the last) as long as it is just: crack down on tax evasion and target the rich. But I'm afraid they will cut my pension instead," said 70-year-old Dionysis Samaros who uses his 720 euro monthly payment to support himself and his family. "How will we make ends meet?"
Annual November 17 marches have often been marred by violence between hooded protesters and police, who will flood the streets with 7,000 officers.
The afternoon march will wend its way past shuttered stores in central Athens to the embassy of the United States, which protesters blame for supporting the six-year dictatorship.
Unions have repeatedly organized protests in the two years since Greece requested its first international bailout, the latest of which attracted more than 100,000 people and sparked fights between protesters that injured at least 70.
Ilias Iliopoulos, general secretary of public sector union ADEDY, said the protest was a first step in a tough battle.
"Even if they don't take new measures, putting in place the latest austerity will bring Greeks to their knees," he said.