The death came just after kickoff at about 13:30. in the 49ers' 34-28 win over Green Bay, police said, and multiple witnesses reported the man appeared to be intoxicated before he fell to a sidewalk.
The death happened the same day a railing collapsed at the Colts' game against the Raiders in Indianapolis, injuring two fans who had been leaning against the barrier above the tunnel leading to Oakland's locker room. It appeared both fans in Indiana escaped serious injury, stadium officials said.
In San Francisco, police spokesperson Gordon Shyy said off-duty medics and police officers gave the man first aid until an ambulance arrived, but he was declared dead from his injuries. Authorities said he appeared to be in his 30s, and his name has not been released.
In a statement, 49ers spokesperson Bob Lange confirmed the team had learned of the accident outside the stadium.
"We would like to express our deepest condolences to the family during this difficult time," he said.
It was not clear how far the man fell from the Jamestown walkway, which goes around the outside of Candlestick.
The historic sports complex closes after this season and will be replaced by a shopping centre. Next year, the 49ers will move into a $1.2 billion stadium at the team's Silicon Valley headquarters in Santa Clara.
Since 2003, there have been more than two dozen cases of fans falling at stadiums across the United States, according to the Institute for the Study of Sports Incidents.
Most recently in Atlanta, baseball fan Ronald Lee Homer jnr died last month after a tumble over Turner Field's fourth-level railing. Homer's death was the third at an Atlanta stadium in the past year.
Also last month in Denver, Broncos fan Noel Robinson was injured when he fell from an escalator at a pre-season game.