[3] Bullock was educated at Winchester College, where he was a member of the school's Ice Club along with Mallory who was his climbing partner.
[4] In 1905, he joined Mallory and the Winchester schoolmaster Graham Irving in the Pennine Alps where they reached the summit of the 4,356-metre (14,291 ft) Dent Blanche.
[6]: 279 Shortly before the 1921 Everest expedition was due to embark, one of the climbing team was asked to drop out and Mallory suggested Bullock as a replacement.
[6]: 155 The Foreign Office rejected Younghusband's request to grant leave to Bullock, who was in Lima at the time, to join the expedition but he gained a special dispensation from the British Foreign Secretary, Lord Curzon, so he could have leave on half pay until the end of 1921 but with no chance of this being renewed.
[13]: 6–24 Later Bullock, on a one-man expedition, reached the Lho La pass from which he photographed the Khumbu Icefall for the first time.
This approach led them to discover the Lhakpa La, where they found there was an intervening valley, the East Rongbuk Glacier.
[6][13]: 27–35 [14] Bullock was reunited with his wife at Lachen in the Teesta valley in Sikkim on 8 October and they eventually sailed home from Bombay.
[16]: 81–82 In 1961 Graham Irving considered that Bullock had never received his fair share of the credit for the success of the expedition.
[6]: 460 Jeffrey Archer's 2009 novel Paths of Glory contains a major character "Guy Bullock" (as well as a "George Mallory").