Denis Adrian Pritchard was born in Sydney, the son of William and Florence Pritchard. From Hayfield Preparatory School and Sydney Grammar School he went to the University of Sydney to study science, graduating BSc in 1916. Rejected for active service in World War I, he worked in munitions and later entered the faculty of medicine. After graduating in 1923 he joined the RAN and remained a naval medical officer from that time until his death. Aware of the importance of postgraduate education he took steps to further his own professional status by acquiring the DTM and the MRCP. By 1934 he had been promoted to surgeon commander and in 1938 he was elected a foundation Fellow of the RACP.

During World War II he saw ocean-going service in a number of ships between 1939 and 1944. On the cruiser HMAS Australia he participated in the Battle of the Coral Sea in May 1942, a naval and air engagement which marked the first real change in the fortunes of the allied forces in the Pacific area by turning back a Japanese invasion fleet aimed at Port Moresby. In January 1946 he was appointed Director of Naval Medical Services with the rank of surgeon captain, following Surgeon Captain WJ Carr (q.v) who was retired with the rank of surgeon rear-admiral. Pritchard was promoted to surgeon rear-admiral in 1953, the first medical officer to attain this rank on the active list. He continued as DNMS until his death which occurred only six weeks before his sixtieth birthday, when he was due to retire.

Pritchard was a quiet, reserved person and because of his reserve was regarded by some as aloof and even a little difficult. He was a good doctor, but was always a naval officer in outlook, a disciplinarian and a stickler for the rules. His service to the Navy was of a high order, particularly in changing the medical service from a wartime footing and re-establishing the peacetime Royal Australian Naval Reserve. It was tragic that he did not live to see the full result of his magnificent efforts. He was at one time honorary physician to the Governor-General (HRH the Duke of Gloucester). He was honorary physician to HM King George VI from 1946 to 1951 and to HM Queen Elizabeth II from 1952 until his death.

Privately he enjoyed his garden and was an authority on camellias. He was an excellent cabinet maker and these two hobbies took up much of such spare time as he had. He married Mary Portis, daughter of the Reverend Canon Harold Portis in 1929. They had one child, a daughter.