The bird was found dead in the Glenveagh National Park in February
A female golden eagle found dead in Glenveagh National Park, Donegal, on 16 February had been poisoned.
The Golden Eagle Trust said tests confirmed the bird was poisoned by what they believe was baited meat.
The Irish government is now considering banning poisoned baits following several deaths of the bird which was specially reintroduced in Ireland.
Environment and Heritage Minister John Gormley expressed his "concern and disgust" about the death of the eagle.
"This is not the first case of poisoning of a rare reintroduced bird in Ireland," he said.
In 2008 a white-tailed eagle was also killed after eating poisoned bait in County Kerry.
Farmers use poisoned bait in Ireland against unwanted animals at various times in the year.
Mr Gormley said his ministry was drafting proposals to regulate the use of poisoned meat-based bait.
Lorcan O'Toole, Golden Eagle project manager said the team have the full support from the Irish Farmers Association in Donegal to tackle the problem of "indiscriminate use of poison."
"Such a concentrated loss of birds represents a real threat to the potential success of the entire project," he said.
Imported golden eagles from Scotland are set free every year in the Glenveagh national park in Donegal.
Golden eagles were last bred in Glenveagh in 1910 and became extinct in Ireland in 1912.