[1][2] He served as the president of the American Medical Association in 1897–98 and as chief surgeon of the Sixth Army Corps in 1898, seeing service in Cuba during the Spanish–American War.

[2][3][4][5] He was involved in experimental research, particularly of acute pancreatitis,[5] plastic surgery, head and neck oncology, the intestinal tract,[6] and the treatment of leukaemia with x-rays.

[2] Senn was born in Buchs, canton of St. Gallen, Switzerland and emigrated to the United States with his family in 1852 when he was eight years old, settling in Ashford, Wisconsin.

[8] Senn published 25 books as well as numerous papers and essays during his career,[2] including the 1886 paper Surgery of the pancreas as based upon experiments and clinical research,[5] and the books Four Months Among the Surgeons of Europe and the Nurse's Guide for the Operating Room.

[4] Throughout his career, Senn amassed a collection of 10,000 volumes and 14,000 pamphlets and articles dating from the 1500s onwards on medicine and surgery, which has been stored in the John Crerar Library.

He also purchased the 7,000 volume collection of old and rare medical books left by a prominent doctor in Germany and donated the materials to the Newberry Library.