The club said Doughty was found in the gym at his Lincolnshire house.
"It is with enormous sadness that Nottingham Forest announce the death of the club's owner Nigel Doughty," the club said in a statement.
"Mr Doughty, who was 54, was found dead earlier today in his gym at his home in Skillington, Lincolnshire.
"The club would like to appeal for the privacy of Mr Doughty's family to be observed at this sad time.
"The club will be making no further comment."
Life-long Forest fan Doughty stepped down as chairman in October after a decade in the job following the sacking of former England manager Steve McClaren.
He was replaced in the role by former Forest player and manager Frank Clark.
Doughty, who saved the Reds from administration when he bought the club for ?11million in 1999, has invested almost £100million of his personal fortune in the club.