Three marches from different hospitals met together at Belfast City Hall.
The four main teaching unions come together to take part in the strike action, along with workers from some healthcare unions.
A rally was also held outside the Guildhall in Londonderry.
The teaching unions are undertaking a 12-hour strike action from midnight to noon on Tuesday.
Schools will reopen at noon to provide free school meals.
Oakwood School in south Belfast was among those where staff manned picket lines on Tuesday morning.
Addele Lynas has been a teacher at the school for 29 years, and said that while taking part in a strike is hard for teachers, they have to do it to secure fair pay.
"I have been a special teacher all my life, the children are so important to me, I love every one of them, they're like part of my own family, but I feel I have to strike because the budget cuts in our school are ridiculous," she said.
"We don't have enough money to spend on anything, but as well as that, as a person, my wages have gone down in real terms by 38%. I'm a single income family and I need, like everybody else, money to pay bills, bills that are going up and up, and my wages haven't.
"Although I love the children, and it's really hard to be here, it is important for workers everywhere to be here."
She said that while a 12% increase sounds like a lot, teachers' wages have gone down by 38% in real terms.
"We just want fair pay for a fair job, we love our jobs, we're here because we love the children, we want to be in the school with the children," she said.
Ian McGonigle, NEU NI president, said teachers are also striking for the future of the teaching profession and their colleagues.
The NASUWT union said teachers are calling for a 12% increase in salaries.
The Education Authority (EA) said active engagement has been taking place for many months between management and the Teachers' Negotiating Committee (TNC) on a pay settlement for 2021/22 and 2022/23.
"However, it is important to note these negotiations are taking place at a time of growing and unprecedented financial pressures within the education sector which continue to adversely impact schools, staff and ultimately children and young people," an EA spokesperson said.
Management side remains committed to continuing meaningful, active engagement with trade union colleagues to reach a resolution and ensure our teachers are fairly remunerated."
The healthcare unions are continuing the industrial action that began in the last few months as part of an ongoing dispute over pay and conditions.
The Nipsa union said thousands of its members in the health service are taking part in a 24-hour strike. They include workers in domiciliary care, social work, ambulance workers, administration and nursing staff.
Padraig Mulholland, Nipsa deputy general secretary, said action by education and health workers is a "warning to employers that workers are not prepared to accept real-terms pay cuts and the destruction of services".
"We must have inflation-busting pay rises for all health service workers and an end to the chronic understaffing that puts lives at risk," he said.
"We cannot have a decent health service if thousands of posts are vacant and the staff are living in poverty.
"It is time for the whole trade union movement, public and private sector, to join together to fight to improve living standards and to defend services.
"Patient safety remains very important for health staff who will take industrial action. Discussions are ongoing to ensure the employers take the necessary steps to protect patients during the dispute."
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