The former opposition leader had never talked publicly about the condition during the 12 years his wife Flor (66) has suffered from it.
However, during a hugely emotional television interview he described how she has lost all mobility and is now in the final stages of the devastating disease.
At the age of just 54, Mrs Noonan began to forget things, the Limerick TD explained to Pat Kenny on The Frontline.
"She'd lose her keys, she'd forget to bring her handbag with her. She'd go shopping and she couldn't find the car in the car park," he said.
Doctors thought that she was suffering from depression and that this was causing short-term memory loss, but Mr Noonan said: "It was a concern she always had because her mother had died of Alzheimer's and it was in her head that there was a possibility so we were all very alert when she began to forget things."
He added: "She was worried, she was very worried and she was tearful ... She used to ask had she but what you tended to do was tell her she hadn't."
The private battle for the Noonan family was getting worse during his period as Fine Gael leader between 2001 and 2002.
"There was a lot of stress in the family," he said, adding: "Flor took a full part in the 2002 general election. When I was out around the country doing the leader things she was working at home and out canvassing every night."
Mr Noonan held back the tears as he outlined how he concluded that his wife had to be moved from the family home to a nursing home.
She had begun to suffer from seizures that were similar to epileptic fits and the family decided to get help from a home with a dedicated Alzheimer's unit in Askeaton, Co Limerick.
A clearly emotional Mr Noonan recalled the fright he got on the first day that she collapsed.
"The first morning I was showering her ... she fell out through the shower door and I couldn't catch her and she was lying on the floor.
"She was unconscious for about three quarters of an hour while we were waiting for an ambulance to come. That happened three times over a two-month period. We just couldn't carry on."
Mr Noonan continued: "When I visit her in the nursing home, she'd smile, and it's a recognition. She responds to music all the time. She responds to smiling faces. She can't communicate."
The politicians thanked the Alzheimer's association for the help they have provided to his family and said he was speaking publicly to raise awareness on their behalf.