The austerity package is expected to scrape through when the vote is held later in the night. But any defections or abstentions could severely weaken the conservative-led coalition formed in June.
"Today we face the most critical decision any government has taken in the past 37 years," Samaras said. "Many of these measures are fair and should have been taken years ago, without anyone asking us to.
"Others are unfair — cutting wages and salaries — and there is no point in dressing this up as something else," he said, adding that the country was, however, obliged to take them.
The alternative is bankruptcy, triggering financial chaos as the country would likely have to leave the 17-country euro bloc.
"The alternative is much worse than any of these measures," said Samaras.
The government combined has 176 of Parliament's 300 seats, and needs a simple majority of those present to pass the bill. Without the Democratic Left, which has said it will vote against, Samaras' conservatives and the Socialists control 160 votes. However, there is a threat of more dissenters, particularly from the Socialist party.
Greece's next bailout loan installment of €31.5 billion, out of a total of €240 billion, is already five months overdue. Without it, Samaras says, Greece will run out of money on Nov. 16.
If Athens cannot raise sufficient funds otherwise, it will quickly find it impossible to pay its huge debts. As well as pushing the country out of the euro, this could trigger a nightmare of bank runs, hyperinflation and currency depreciation that would vaporize savings and put many basic goods out of the reach of many Greeks.
The measures are for 2013-14 and include new, deep pension cuts and tax hikes, a two-year increase in the retirement age to 67, and laws that will make it easier to fire and transfer civil servants who are currently guaranteed jobs for life.