Household budgets are stretched while elite pensions remain "gold-plated", Irish Congress of Trade Unions assistant general secretary Peter Bunting said.
Many schools and colleges closed and hospitals postponed operations in the dispute over Government cuts and future pension provision. There was also no public transport.
Thousands of public-sector workers across Northern Ireland were participating in the most widespread action for more than three decades.
Mr Bunting told crowds at Belfast City Hall: "The public sector is being sacrificed in the name of an ideology which favours the 1%."
The protest is against UK Government plans to increase the amount of money public-sector workers pay into their pension, raise the retirement age to 67 and introduce career-average pensions.
Higher contributions are due to be phased in over three years from April 2012, amounting to an average 3.2 percentage points more in each employee's contribution rate.
Ministers argued that change was needed because people were living longer and said the cost of public-sector pensions to the taxpayer had already gone up by a third.
Unions said the changes would mean people working longer, paying more and getting less - and pointed to forecasts that the cost of pensions would drop as a share of GDP by 2060.
Employers' organisation the CBI said the biggest impact on the private sector was people not being able to get to work because of disruption to public transport or parents having to stay at home to look after children due to school closures.