Min Bahadur Sherchan died at the Everest base camp on Saturday evening but the cause of death was not immediately clear, said Dinesh Bhattarai, chief of Nepal's Tourism Department.
Mountaineering official Gyanendra Shrestha, who is at the base camp, said the cause was likely cardiac arrest but he could not elaborate due to a poor telephone connection.
Sherchan, a grandfather of 17 and great-grandfather to six, first scaled Everest in May 2008 when he was 76 — at the time becoming the oldest climber to reach the top.
His record was broken in 2013 by 80-year-old Japanese climber Yuichiro Miura.
Before leaving for the mountain last month, Sherchan told The Associated Press that once he had completed the climb and became famous, he intended to travel to conflict areas to spread a message of peace.
He had trained for months before the attempt, saying that he did not suffer from any respiratory problems and his blood pressure was normal.
Being born in the mountains, he said he had did not have any problems with high altitude or the low levels of oxygen there.
Sherchan's love of mountaineering began in 1960 when he was assigned by the Nepalese government to be a liaison officer for the Swiss team climbing Mount Dhaulagiri.
He later became an apple farmer and constructed roads and dams before settling down to run hotels in Kathmandu.