Schreiber was born in Berlin to Paul Schreiber (a postal inspector) and his wife Gertrud Kettlitz. After completing gymnasium in Berlin, he studied medicine at the universities of Berlin, Tübingen, and Greifswald. In 1914, he enlisted voluntarily for military service and served with the 42nd Infantry Regiment in France. He was injured at the First Battle of the Marne. After his recovery, he continued with his studies and served as a temporary doctor on the Western Front until the end of the war in 1918. In 1920, he graduated Dr. med. from the University of Greifswald. In 1933, he joined the Nazi Party.
Schreiber was in charge of developing vaccines for the Wehrmacht, in particular to guard against biological warfare agents in association with the Third Reich's own development of such weapons. In October 1942, Schreiber attended the conference where the results of human experiments at Dachau were presented. In May 1943, he headed the third session of the advisory specialists of the Armed Forces. In September 1943, Schreiber accepted the position of the commander of the Training Division C of the Military Medical Academy. In 1944, Dr Schreiber conferred with Dr. Karl Brandt, the attorney for health care, scientific advisory board.
In 1945, he was taken prisoner of war by the Red Army in Berlin and taken to the Soviet Union. On 26 August 1946 Schreiber appeared as a surprise witness at the Nuremberg Trials, giving evidence in support of the Soviet Chief Prosecutor, Roman Rudenko, primarily against Kurt Blome, his deputy who had been in charge of offensive biological weapons development. A recording of his testimony at the trial can be found at the online archive of the Imperial War Museum. The transcript became part of the Nuremberg proceedings against German major war criminals.
In fall 1948, Schreiber reappeared in the West with his wife, his son and one of his adult daughters. In a press conference on 2 November, he explained that he had initially been held in Lubyanka Prison but had later been moved to a series of safe houses in the Soviet Zone of Germany, where he lived with and provided medical care to other former Nazi generals, was given the rank of starshina, and was ultimately offered the position of Chief Medical Officer in the newly formed East German Police Force, the Volkspolizei. Rejecting this position, he said he had been offered a professorship at the University of Leipzig but demanded the University of Berlin; after which, seeing an opportunity, he had evaded his handler and on 17 October taken a train from Dresden to Berlin and presented himself to the Allied military authorities in West Berlin. Schreiber was hired to work with the Counter Intelligence Corps and beginning in 1949 was employed as post physician at Camp King, a large clandestine POW interrogation center in Oberursel, Germany.
Schreiber was subsequently taken to the United States as part of Operation Paperclip. He arrived in New York on September 17, 1951, on the USNS General Maurice Rose, (T-Ap216) with his wife Olga Conrad Schreiber, his son Paul-Gerhard Schreiber, and his mother-in-law Marie Conrad. The manifest of the ship does not list travel documents for them, but declares them to be "Paper Clips".
On 7 October 1951 the New York Times reported that he was working at the Air Force School of Medicine at Randolph Air Force Base in Texas. A notice also appeared in a medical journal and was seen by Leopold Alexander, who had been an expert consultant at the Nuremberg Doctors' Trial. He contacted the Boston Globe, and the resulting publicity by Drew Pearson and other journalists concerning Schreiber's Nuremeberg evidence and tying him to abusive experiments performed by his subordinates on concentration camp inmates, such as Janina Iwańska and the other "Ravensbrück rabbits", led to a public outcry. Schreiber's contract was not renewed. He left Texas for the Bay Area of California, where one of his daughters now lived, and after the Joint Intelligence Objectives Agency arranged a visa for him through an Argentinian general, and he was provided with moving funds for himself and his family, on 22 May 1952 they were flown on a military aircraft to New Orleans and from there flew to Buenos Aires, to join his other daughter.
In Argentina, he worked at an epidemiological laboratory and researched his ancestry; family documents state that he wished to prove he was descended from the royal house of Prussia. He died on 5 September 1970 in San Carlos de Bariloche, Río Negro, Argentina.
- McCoy, Alfred. "Science in Dachau's Shadow: Hebb, Beecher, and the Development of CIA Psychological Torture and Modern Medical Ethics". Journal of the History of the Behavioral Sciences, Volume 43 (4), 2007.
- Transcripts, Trial of German Major War Criminals Nuremberg, Germany, August 26, 1946.
- Annie Jacobsen, Operation Paperclip: The Secret Intelligence Program that Brought Nazi Scientists to America, New York: Little, Brown, 2014. ISBN 978-0-316-22105-4, pp. 7, 164–65.
- Jacobsen, pp. 232–39.
- Linda Hunt, Secret Agenda: The United States Government, Nazi Scientists, and Project Paperclip, 1945 to 1990, New York: St. Martin's, 1991, ISBN 9780312055103, p. 89.
- International Military Tribunal, Nuremberg: Day 211 26/8/1946 Walter Schreiber questioned. Audio Recordings, Imperial War Museum, London.
- Jacobsen, pp. 322–30.
- Jacobsen, pp. 331–33.
- Jacobsen, pp. 348–56.
- Jacobsen, pp. 361–63.
- Hunt, p. 90.
- Jacobsen, p. 363.
- Family tree, Ancestry.com.