[1] His first major client was Oliver Perry-Smith, an American climber who hired Knubel to guide him through the Alps in 1903; together, they ascended the Matterhorn, Wellenkuppe, Zinalrothorn, Weisshorn, Lyskamm, Ober Gabelhorn, Dent Blanche, and Täschhorn.
His mountaineering skills were noticed by British climber Geoffrey Winthrop Young, who hired Knubel as his guide.
In February 1920, Knubel and Marcel Kurz, using skis, made the first winter ascents of the Wellenkuppe, Ober Gabelhorn, Schallihorn, and Täschhorn.
Throughout his career, he made over 800 ascents of Alpine peaks higher than 4,000 metres (13,000 ft) ("four-thousanders") and led around 120 clients.
He died at Visp on 31 May 1961 after undergoing abdominal surgery—related to an episode of appendicitis earlier in his life—and was buried at his hometown of St.