In 1874, Duhamel founded the Isère or Grenoble section of the Club alpin français (French Alpine Club) and began to explore the peaks of Dauphiné. In 1875, in the company of Baron Emmanuel Boileau de Castelnau and the guide Alexandre Tournier, Duhamel tried to climb the western peak of the Meije without reaching the summit. A second attempt the following year by the south side led to the foot of a wall deemed impassable. Finally in 1877 Boileau de Castelnau and his guide Pierre Gaspard reached the top, taking the first path traced by Henry Duhamel. Henry Duhamel turned to other peaks, both in France and Kabylie, and established twenty-three new routes, including first ascents of eight virgin peaks. He climbed the Pic Gaspard (3883 m) in 1878 and the south face of the Barre des Écrins (the south arête of the Pic Lory, 4088 m) in 1880 with Pierre Gaspard and his son.