Guthe immigrated to the United States in the summer of 1892 to marry Clara Belle Ware (1867-1947), from Grand Rapids, Michigan. The couple met during Ware's visit to Germany in 1890-91. In 1893 he obtained a position as instructor in physics at the University of Michigan, and in 1900 was promoted to Assistant Professor. In 1903, Guthe took a position as Assistant Physicist at the then newly established National Bureau of Standards in Washington, D.C. (now the National Institute of Standards and Technology). In 1905 he accepted an invitation to become Professor of Physics and Chairman of the Physics Department at the University of Iowa. Guthe was a member of the jury of awards at the St. Louis Exposition in 1904 and was vice president of the American Association for the Advancement of Science in 1908. In 1909 the University of Michigan solicited Guthe to return as a full Professor in the Physics Department, and he moved back to Ann Arbor with his young family. In 1912 Guthe was named Dean of the newly formed Graduate School at the University of Michigan.