The emergency department at Daisy Hill Hospital is due to open by the end of next month, health bosses have said.
It is hoped the move will help reduce the number of people who have been waiting longer than 12 hours in the casualty unit at neighbouring Craigavon Area Hospital.
Latest Department of Health figures show that it was the worst performing emergency department in Northern Ireland in June.
According to the statistics, 551 people waited longer than 12 hours to be admitted or treated and discharged at the hospital's A&E in June.
Along with a number of other health services here, the Daisy Hill unit was closed earlier this year in preparation for a surge in Covid-19 cases. There were concerns the move would become permanent.
However, the Southern Trust said: "We are working to safely reopen the emergency department at Daisy Hill by the end of September.
"The trust will widely publicise the reopening arrangements in the coming weeks."
SDLP MLA Colin McGrath, a member of Stormont's health committee, welcomed the commitment by the Southern Trust to reopen A&E at Daisy Hill.
"I would question that it ever needed to be closed at all and I believe that the people of Newry, Mourne and Down were adversely and disproportionately impacted as a result of the decision to close the emergency department," he said.
"I was deeply unhappy with the decision. However, it is a welcome development that they are looking to reopen it.
"I know this comes at a time when there are more cases of Covid-19, so I hope that the date for opening isn't pushed back as a result.
"We saw last week where 15 staff had to isolate at the emergency department at Craigavon after a colleague was diagnosed with Covid-19.
"This sort of thing is going to continue to happen and it makes sense to me that services are spread out across sites to reduce the impact when someone unfortunately tests positive with the virus.
"Ultimately, the number of patients attending emergency departments is unlikely to reduce without a fundamental review of how we deliver services, and by closing a unit you are simply moving them onto the next unit."
This issue arose following the closure of the Daisy Hill unit, with the public going to Craigavon Area Hospital and the Royal Victoria Hospital instead, with wait times at both units rising as a result.
Elsewhere, the number of people attending A&Es across the region is on the rise. However, space inside the units remains limited due to the safety measures in place to deal with Covid-19. The Royal College of Emergency Medicine has repeatedly warned there are not enough hospital beds in the system to cope with demand.