Danielli hasn't played international rugby since last year's World Cup while he has only made seven appearances for Ulster in all competitions since then.
The problem hampering Danielli is a debilitating back injury and, while retirements falls on him hard, he couldn't think of anything else to remedy the situation.
"Having been advised that I am no longer able to achieve the level of fitness required to play professional rugby, it is with great sadness that I announce my retirement from the game," said Danielli.
"This last year has been incredibly frustrating in that my back has not allowed me to train or play anywhere near a frequency or an intensity necessary in a professional game.
"And because of the pain, deterioration and related injuries it's causing, I have to think about later life beyond rugby. Having said that I feel privileged to have been playing for over a decade.
"I have thoroughly enjoyed my time as a professional rugby player, particularly my last five years here at Ulster and the huge honour of representing my country."