By 1910 Marie-Antoinette was widowed and wealthy and living in Paris and when her other son died she persuaded Auguste to join her there. As he had no French dental qualifications, Auguste Valadier studied at l'Ecole Odontotechnique de Paris from November 1910 to June 1911 and received the certificate of Chirugien Dentiste (Tr. Dental Surgeon) from the Faculty of Medicine of the University of Paris in July 1912. After that he was permitted to practice in France. In July 1913 he married Alice Wright, the granddaughter of Robert Clinton Wright, a former United States Minister in Brazil.
In October 1914 Auguste joined the British Red Cross Society (BRCS) in Paris who sent him to Abbeville. “The History of the Great War” (1922) records: "Dental surgeons commenced to arrive in France in early November and were allocated to clearing hospitals and to the bases. An eminent dentist, M. Valadier, a citizen of the United States, who had been sent from Paris to Abbeville by the BRCS, was also accepted for duty with the British troops on 29 October."
Auguste appears to have been the first dental surgeon to provide dental treatment for the British troops in France. The dental surgeons sent over by the War Office were given temporary commissions while attached to the Royal Army Medical Corps, and Auguste Valadier was gazetted as an honorary Lieutenant, and in 1916 was promoted to the rank of Major.
By early 1915 Auguste had set up a 50-bed oral surgery unit attached to the 83rd (Dublin) General Hospital at Wimereux for the treatment of facial injuries. Much of this reconstructive work was paid for out of his own pocket, while the staff in his dental laboratory in Paris fashioned the appliances necessary for the treatment of severe injuries to the jaw. As he was not a surgeon himself it was considered necessary that Auguste would require the assistance of a trained surgeon in the operating theatre and Harold Gillies joined his team. It is uncertain how long Gillies worked with Auguste, but it was certainly long enough to inspire in Gillies the interest to learn more about this radical new medical treatment.
When the war ended Auguste applied for and received the 1914 Star, the British War Medal and the Victory Medal with three Mentioned in Despatches (MiD) emblems. In February 1920, in recognition of his service during the War, Auguste Valadier was made a Knight Commander of the Order of the British Empire by the British government. However because he was a French national the award was purely honorary. He had been appointed a Companion of the Order of St Michael and St George (CMG) in June 1916 and an Associate of the Order of St John of Jerusalem in January 1917. In 1919 he was made a Chevalier of the Legion of Honour by the government of France.
Auguste Valadier applied for British citizenship and in recognition of his service to the British Army it was granted on 16th March 1920. He was finally knighted by George V on 8th March 1921.
During the 1920s Auguste went back to his dental practice in Paris where he became President of the American Dental Club of Paris.
Auguste died on 31st August 1931.
Major Sir Auguste Charles Valadier at No.13 Stationary Hospital. 6th October 1916