 Hallwachs became a professor at the Dresden University of Technology in 1893, originally for electrical engineering until he succeeded August Toepler in 1900 as a professor for physics.In 1921/22 Hallwachs was rector of the university.In 1890 Hallwachs married Marie Kohlrausch, the daughter of Professor Friedrich Kohlrausch (physicist); he was an assistant with her in Würzburg.