An ambulance was called after the supporter fell seriously ill just before the conclusion of the Super League clash against Wigan Warriors at the Yorkshire club's Belle Vue ground.
He has been named by the club as John Metcalfe, 84, from Crofton.
Paramedics attempted to resuscitate Mr Metcalfe, according to onlookers, while the ambulance remained in one of the corners of the pitch.
But it has been confirmed that he later died.
Michael Carter, the Wakefield Trinity chairman, said on Twitter: "Devastated to hear of the passing of life-long Trinity fan John Metcalfe at the end of yesterday’s game. Sincere condolences to all family."
An official statement from the club said: "Wakefield Trinity are deeply saddened to hear of the passing of a life-long fan at yesterday’s game.
"John Metcalfe, who was 84 and lived in Crofton, will be sadly missed by all his family and friends and the club wish to send their deepest condolences at this time."
Several other supporters shared their condolences online, including Rich Bentley, who Tweeted: "Terrible news. Well done to everyone who tried to save him. My thoughts are with his family and friends as this awful time."
Yesterday's game was Wakefield's last of the season. They beat Wigan Warriors 32-0.