The Silicon Valley entrepreneur and SurveyMonkey chief executive Dave Goldberg died of severe head trauma, according to local officials.
Mr Goldberg, 47, husband of Facebook executive Sheryl Sandberg, was found lying next to a gym treadmill on Friday at a Four Seasons resort in Mexico.
Mexican authorities have no plans for a criminal investigation.
The officials said Goldberg still had vital signs when he was discovered, but later died at a hospital.
He reportedly left his room in the resort near Nuevo Vallarta at 16:00 local time to exercise, and family members went to look for him when he failed to return.
He was found at about 18:30 in the gym, lying by a treadmill, with a blow to the lower back of his head.
It was apparent he had slipped on the treadmill and hit the machine, a spokesman for the Nayarit state prosecutor said.