Mr Mansfield, best known as the owner of the Citywest hotel, conference and golf complex, had been ill for some time, and died this morning.
He was in his mid 70s.
He died at his home in Saggart at about 7:30am.
His son Tony has told Independent.ie that he had been suffering from Multiple System Atrophy (MSA) in recent years and took a turn for the worse two days ago.
Mr Mansfield’s sons are today gathered at the family home comforting their mother Anne.
Mansfield grew up in Brittas, Dublin.
When he left school he bought a lorry and set up a haulage business and grew his business from there. He made his fortune selling machinery left over from the Falklands war and it was from this that his empire ranging from hotels to property began.
During the boom, his wealth was estimated in the hundreds of millions, and his assets included the Weston Aerodrome.
The main part of his empire – Citywest – was placed into receivership in 2010.
Separately, Weston Aerodrome was seized by NAMA.
The businessman is survived by his wife Anne and three sons Tony, Jimmy and PJ.