Everest: Japanese Man Oldest To Reach Summit
Yuichiro Miura said: "This is the world's best feeling." But he confessed to feeling "totally exhausted".
Mr Miura had previously conquered the 8,850-metre (29,035-foot) peak when he was 70 and again when he was 75.
The climber and his son Gota called their support team from the summit to report the news. They reached the peak at 9:05 am local time.
Japanese public broadcaster NHK showed Mr Miura's daughter Emili talking to them on a speaker phone in Tokyo. She clapped when her brother told her they had reached the top.
The climbers planned to stick around the summit for about half an hour, take photos and then start to descend.
Before him, the oldest person to reach the top of the world's highest mountain was Nepal's Min Bahadur Sherchan, who accomplished the feat at the age of 76 in 2008.
Mr Sherchan, now 81, is preparing his own attempt on the summit next week, meaning Mr Miura's record may soon be broken.
On his expedition's website, Mr Miura explained his attempt to scale Everest at such an advanced age.
"It is to challenge (my) own ultimate limit. It is to honour the great Mother Nature," he said.