Hartwell graduated from Yale in 1892, holding both PhD and MD degrees, and began a career as a surgeon in New York City. He also continued with football as a coach. He served as the head football coach at Lehigh University in 1892, the United States Naval Academy in 1893, New York University in 1894, and at his alma mater in 1895, compiling a career college football coaching record of 21–12–2. Hartwell's 1895 Yale squad went 13–0–2 and was later recognized as a national champion by Parke H. Davis.