Around 4,000 members of the union will take part in the action at health and social care workplaces across Northern Ireland.
Emergency cover will still be provided.
A second day of strike action is also planned for Thursday, March 16.
The union said workers, including ambulance service staff, are fighting for a fair pay rise and urgent action to avert an “existential crisis” in the service.
The strike follows a ballot across all five health trusts and the Northern Ireland Ambulance Service which returned an average 87 per cent vote in favour of strike action.
Unite general secretary Sharon Graham said: “Unite’s members’ overwhelming vote for strike action signals their determination to secure a cost of living pay increase and safe staffing for patients.
“With chronic low pay making it impossible to recruit and retain essential health workers, the health service in Northern Ireland is facing an existential crisis.
“In the absence of a functioning Stormont executive, the responsibility for resolving this dispute falls to the UK government. The PM and ministers have been missing in action but it is their job to ensure that NHS bosses make a realistic offer to the workers who keep our health and social care services running. They must get on and do so without delay.”
Unite’s lead regional officer for health in Northern Ireland Kevin McAdam said: “Nobody should be in any doubt regarding our members’ determination to defend their living standards amid an unprecedented cost of living crisis.
“Our members will be joining members of other health trade unions on the picket lines tomorrow and, unless sense prevails and our members are made a better offer, there will be a second day of strike action on March 16.”
Unite members will also be joining striking health workers from other health trade unions in marches to Belfast City Hall and other rallies across Northern Ireland in a show of solidarity for striking education workers.
‘Our combined action is a warning to employers that workers are not prepared to accept real terms pay cuts and the destruction of services’
— Armagh I (@ArmaghI) February 20, 2023