Boyd Penfold was born at Rowlands Gill, just outside Newcastle-upon-Tyne, the son of William James Penfold and Annie (nee Liddell). His father was a medical graduate from Edinburgh University and became a research worker at the Lister Institute. In 1917 the family moved to Australia where Dr WJ Penfold had been appointed director of the newly established Commonwealth Serum Laboratories.

Boyd was educated at Scotch College, Melbourne. On leaving school he decided to study medicine but did not have the prerequisite subject of Latin. He commenced veterinary science but was able to transfer at the end of the first year. He was a conscientious student and came second in the class list at the final examinations with second-class honours in medicine, obstetrics and gynaecology. After a residency at the Alfred Hospital he entered the Baker Institute which was now under the directorship of his father, WJ Penfold. Here he was appointed a helminthologist and researched for two and a half years, producing thirteen publications and material that later was accepted as an MD thesis. He was awarded the Bertram Armytage Prize for medical research in 1937. During this period he married his university sweetheart, a Canadian, Mary Aotea Campbell.

His main interest was clinical medicine so he left the Baker Institute and set up in general practice in Richmond on the Hill. His practice soon blossomed. He read widely and kept abreast of modern developments. In the Second World War he joined the AIF, attended a six month course at the School of Tropical Medicine in Sydney, then worked as a pathologist in different army hospitals in Queensland.

After returning to private practice his enquiring mind and enthusiasm for clinical medicine directed his energies towards becoming a physician. He passed the Membership in 1946 and set up in Collins Street as a consultant physician and clinical pathologist. This brought him into the expanding field of blood transfusion and in the early 1950s he was using more blood from the Central Blood Bank than any other individual or institution, apart from the Royal Melbourne Hospital. He did the first exchange blood transfusion for Rhesus incompatability in a newborn in Victoria. Surgery was expanding at a great rate at this time, and he added another string to his bow as a resuscitationist to a number of busy surgeons around the City. Even in his later years it was common for him to be called out late at night to help resuscitate someone after a surgical mishap.

Medicine was his life. While still in active practice he died suddenly from a myocardial infarct. The huge crowd of patients, nurses and doctors that attended his funeral was testimony to the fact that he was a humble, caring, compassionate and competent doctor.