After holding a series of academic medicine positions, Zinsser became an associate professor at Stanford University in 1910. In 1913, he moved to a position at his "alma mater". At Columbia, he was the doctoral advisor of Rebecca Lancefield, although he did not permit her to physically work in his laboratory due to her gender. Ten years later, Zinsser was hired by Harvard Medical School, where he stayed — except for service in the US Army Medical Corps in World War I — until his death.