Paul Parkinson, 48, suffered a heart attack after months of stress and grief following the murder of his teenage daughter, who was found buried in someone else's grave.
A huge police hunt led to the 17-year-old's body being found in a disturbed grave near her home in Didcot, Oxfordshire in December.
The teenager's former boyfriend, 22-year-old Ben Blakeley, is set to stand trial for her murder on Friday, alongside a 17-year-old boy who is accused of perverting the course of justice.
Ben has pleaded guilty to the manslaughter of Jayden but denies murdering her. The official cause of death was strangulation.
Mr Parkinson had already travelled south for the start of the trial at Oxford Crown Court, when he collapsed and died Thursday.
Relatives have attributed his death to the stress caused by the murder of his beloved daughter.
Parkinson was separated from Jayden's mother, Samantha Shrewsbury, and was said to be estranged from his daughter at the time of her death.
After the plea hearing in March, Mr Parkinson thanked his friends on Facebook, writing: 'Can I just say thank you to all of you for your support (sic). Just got to wait till June now for the outcome.'
He had previously posted in December that he was going to 'get you you scum...no matter how long it takes me.'