The climber was making a rappel in the Subway, a popular and demanding canyoneering route about 250 miles south of Salt Lake City.
His hiking partner was unable to free the man, who was found hanging early Wednesday from a drop-off, Park Superintendent Jock Whitworth said.
Authorities were withholding the man's name and hometown pending family notification. He was from California, and apparently had little experience navigating the Subway. He was caught about halfway in a 9-mile narrow chasm with fast-moving cold water.
His female partner hiked out after some difficulty Wednesday to alert rangers.
It was the first death of a hiker in the Subway in many years - park officials were unable to immediately determine when the last death occurred there, although they are frequently called to rescue distressed hikers.
"We're still investigating it," Whitworth told The Associated Press. "It was not real clear to us what happened."
What is known is that the man bypassed a more gentle descent down a rock slab for a vertical drop-off that left him unable to use his feet to maintain traction with rock, he said.
Hanging in a harness for too long, especially upside-down, can cut off a climber's blood supply, said Mike Banach, a guide who is familiar with the Subway and says many hikers are left at their own peril because commercial guiding is prohibited inside the park - they would compete for a limited number of hiking permits.
"People are going in without knowledge or experience and don't even have the ability to hire a guide," said Banach of Zion Mountain School in Springdale, Utah, the park's main entrance. He guides hikers outside Zion National Park.
Banach said the accident happened at a 30-foot-drop that isn't considered difficult if done correctly. He called the death puzzling.
Whitworth summed up the dangers of the subterranean route in a statement.
"The Subway is deceiving. It is a very popular trail, but very difficult - the 9-mile hike requires rappelling and ascending skills, extensive route finding experience, and swimming through several cold and deep pools," Whitworth said. "Unfortunately, its location inside the wilderness also means that rescues are not always possible or timely enough. Sound decision making and problem solving are critical."