Penhall was involved in a race with Mummery to be the first to climb the Zmutt ridge of the Matterhorn, a race which Mummery eventually won. According to Penhall, his interest in finding a new way up the mountain had been kindled by Edward Whymper's account of the successful first ascent in 1865 in Scrambles amongst the Alps. As Mummery and Burgener approached the mountain to attempt the ridge they met Penhall, and guides Ferdinand Imseng and Louis Zurbrücken, who had retreated from the mountain after a bad-weather bivouac on the ridge. After a brief rest in Zermatt, Penhall returned to the Matterhorn, making the first ascent of its west face on 3 September 1879, a harder climb than the Zmutt ridge; his party reached the summit one hour after Mummery's. Penhall wrote an account of the west face climb in the Alpine Journal entitled 'The Matterhorn from the Zmutt Glacier'. The Penhall Couloir on the west face is named after him.