A helicopter crew retrieved the 49-year-old's body in Val Seriana in the Bergamo region of Italy, ANSA reported.
Merell -- known as an "8,000er" because he was one of the few climbers to climb 10 peaks topping 8,000 meters -- climbed Mount Everest twice and also scaled Makalu, Kangchenjunga, Gasherbrum I, Shisha Pangma and Annapurna.
He had to recover the body of a friend on Annapurna after he was buried by an avalanche in 2005, PlanetMountain.com reported.
"His Himalayan career had reached impressive heights, but the deep roots of the mountain man from Bergamo had remained intact," friend and fellow climber Manuel Lugli said in a written statement on PlanetMountain.com.
"His fall, right in the heart of his mountains, is a tragic symbol of his profound roots, a terrible seal reserved for Mario just as for numerous other great alpinists before him: (Erhard) Loretan, (Patrick) Berhault, (Giuliano) de Marchi," he said.