A pair had bred at a confidential nest site in Co Fermanagh, Ulster Wildlife said.
The charity said the distinctive bird of prey had recolonised naturally in the area and successfully produced at least two, possibly three chicks – the first known wild osprey chicks on the island of Ireland in modern times.
The discovery was made by Giles Knight, environmental farming scheme adviser with Ulster Wildlife.
He has been observing the breeding pair for the last three seasons alongside his local farm visits in the area.
“I have been keeping this news close to my chest for a long time to ensure the safety and welfare of these spectacular but vulnerable birds,” he said.
“Along with my son Eoin, I have watched the adults return to the same site since 2021, so you can imagine my excitement the moment that I saw three chicks and two adults this year.
“It was a rub-your-eyes, once-in-a-lifetime moment; an absolute highlight of my 30-year wildlife career – like finding long-lost treasure.
“With at least two of the chicks fledging this season, this is a huge conservation success story and indicates a healthy wetland ecosystem with plenty of suitable habitat and fish to bring this apex predator back to our skies and plunging into the Fermanagh Lakelands.
“Truly the return of a living countryside.”
Ulster Wildlife said ospreys were thought to have become extinct as a breeding bird in Ireland in the late 18th century due to systematic persecution.
Although often sighted on migration to and from Sub-Saharan Africa, confirmed breeding in Ireland has been elusive until now, with Scotland the UK breeding stronghold.
Dr Marc Ruddock, from the Northern Ireland Raptor Study Group, hailed the “brilliant news”.
“All the signs and sightings in recent years have been pointing towards this, but now actual breeding success has finally been confirmed – truly brilliant news,” he said.
Mr Knight said the location of the site would not be disclosed to ensure the safety of the birds.
“Now these birds are back in Ireland and breeding successfully, it is critical that they are left in peace so their numbers can continue to grow by returning year-on-year to breed. We believe and hope that this could be the start of a raptor dynasty,” he said.
“It has been both encouraging and heartwarming to see the landowner, the local farming community and our partners welcome the ospreys’ return.
“Their ongoing support will enable future generations to enjoy these magnificent birds far into the future.”
Across Ireland, osprey monitoring, the erection of nesting platforms, and planning for translocation and reintroduction programmes have been ongoing for years.