Brown's mountaineering achievements in the Alps and Himalayas included many ascents in the 1950s with Whillans and other members of the Rock and Ice climbing club and, in 1955, the first ascent of the world's third highest mountain, Kangchenjunga in the Nepalese Himalayas, with George Band. In 1956 he made the first ascent of the west summit of the Muztagh Tower in the Karakoram with Ian McNaught-Davis. The other members of the team, John Hartog and Tom Patey, reached the main summit the next day.