Morell worked as a ship's doctor for a year. Then, in 1914, when Germany was fighting World War I, he volunteered to be a doctor for the German army. He worked as a doctor in a German army battalion until 1917. By 1918, Morell had opened his own doctor's office in Berlin. He became popular for treating his patients' illnesses in unusual ways. Both the Shah of Persia and the King of Romania asked Morell to be their personal doctors, but Morell refused.