Ewert was born in Athens on April 10, 1894. He was the son of Police major Miltiades Ewert who was of Bavarian origin. He studied Law at the University of Athens and, in 1915, enlisted in the Police, graduating from the Police Academy in 1920. In 1929, he transferred to the newly-established Urban Police force.
After the capitulation of Greece in World War II, Ewert became Chief of Police in Athens. In this capacity, he saved many Jews by issuing false identity papers to them. After the Germans withdrew from Greece, in December 1944, Communists marched on Athens and held a demonstration in a central square. Ewert ordered his policemen to disperse the crowd by any and all means. This violence was the beginning of the December events ("Dekemvriana") which marred the period following Greek liberation.
Between 1951 and 1955, Ewert served as head of the Greek Urban Police Force. He was forced to resign on January 31, 1955 after disciplinary action was taken against him in a matter involving foreign agents.