Loretan died immediately after a fall from the summit ridge of the Grünhorn, near Bern, at 3,800 metres, reports said.
The accident, which occurred on Loretan’s 52nd birthday on Thursday, also involved a second climber, a 38-year-old Swiss woman, who was flown to hospital and is in serious condition, according to the leading daily Neue Zürcher Zeitung.
Police are investigating the fall, the paper said.
Loretan, originally from the Canton of Fribourg, was considered a top mountaineer after he managed to conquer the world’s 14 highest peaks above 8,000 metres high.
He is also well-known for his 1986 ascent of Mount Everest overnight and without bottled oxygen.
Besides his mountaineering successes, Loretan also grabbed headlines in 2003 when he pleaded guilty and was convicted on manslaughter charges for the death of his baby son.
Loretan was accused of shaking the baby and causing his death.
The case helped raise awareness in Switzerland on the risk of shaking babies even for a few seconds, as the weakness of their neck muscles can lead to accidental death