John Halliday was born in Cooma in New South Wales, the eighth member of a family of thirteen children. During early childhood medical opinion suggested that he was unlikely to survive to adult age. Despite this prediction he was educated at King's College, Goulburn and matriculated in 1916 with first place in the State in Mathematics. He entered Medicine, becoming a student at St. Andrew's College, and was in the last group taught by the original professors of the Sydney University Medical Faculty - Professor T Anderson Stuart, Professor J T Wilson and Professor D A Welsh. On graduation (delayed for a year because of illness) he became an intern at Royal Prince Alfred Hospital in 1923 and the following year an RMO at Prince Henry Hospital where his original interests tended to be surgical.

Following his marriage to Muriel Burkitt, a member of a well known medical family, in 1925, his next six years were spent in a very busy and successful general practice in Muswellbrook. In 1931, in spite of the worldwide depression, a decision was made to go to Britain for training in Internal Medicine. He studied for two years at the London Hospital, the Brompton and Queen's Square among other hospitals, making long-lasting friendships with both teachers and fellow postgraduate students. On return to Australia he sought and obtained posts as Honorary Assistant Physician to Lewisham Hospital, as Official Visitor to the Callan Park Mental Hospital and, in 1935, as Honorary Assistant Physician at Royal Prince Alfred Hospital. His consulting physician's practice grew as he gave his time and experience in the various Out Patients Departments at Royal Prince Alfred Hospital. He was associated with the first use of iatrogenic malaria in the treatment of general paralysis of the insane. His interest in electrocardiography stimulated by his UK experience grew, and he was one of the first physicians in Sydney to make wise use of it.

In 1940 he enlisted in the Australian Army Medical Corps (AAMC), and the munificence of a grateful patient enabled him to take with him to the Middle East a "portable" electrocardiogram which could be used in the field. His medical unit was commanded by John Belisario (qv) and included Bill Morrow (qv), Norman Wyndham and Angus Murray among others. The unit saw service in Eritrea and Persia, and during this time John was involved in cardiological assessment for both the British and Australian Armies, the AIF being under British command. The 2/5th AGH returned to Australia in 1941, John Halliday rising to the rank of Lieutenant-Colonel. The remainder of his army service was in Australia. On discharge he was soon appointed to the then recently established Hallstrom Institute of Cardiology, a special department at Royal Prince Alfred Hospital initiated by Kempson Maddox (qv), Frank Mills and John Halliday with the financial assistance of Sir Edward Hallstrom. He remained attached to this unit until his retirement from the hospital honorary staff in 1959. Affectionately known as "Cat's Ears" because of his auscultatory ability, he became teacher, mentor and a legend in cardiological examination among many of the present senior cardiologists in Australia.

As part of his professional life outside Prince Alfred he was appointed as Medical Officer to the AMP Society in 1946 and succeeded his teacher S A Smith as CMO in 1952, holding this post until retirement from this organisation in 1964. During this association with Insurance Medicine he was, together with his actuarial colleagues, responsible for the introduction of numerical as opposed to age ratings in insuring substandard lives and for the authorship of the AMP Assessment Manual. He was instrumental in establishing the Life Insurance Medical Research Fund of Australia and New Zealand and was its first Medical Director from 1953 to 1959.

To the Royal Australasian College of Physicians he gave long and faithful service, being a Foundation Fellow in 1938, an Elected Councillor from 1958 to 1961, Vice-president from 1964 to 1966, Chairman of the Financial Advisory Committee from 1966 to 1970, Chairman of the Grants Advisory Committee from 1964 to 1966 and NSW State Committee Member from 1958 to 1961. He was a foundation member of the Cardiac Society of Australia and New Zealand in 1952, Chairman of the Scientific Meeting in 1958 and President of the Society from 1962 to 1964. His contribution to the work and expansion of this organisation was enormous. As one of the original organising committee he played a large part in the establishment of the National Heart Foundation in this country, becoming a member of the original National Medical and Scientific Advisory Committee and giving many years of long and fruitful support.

This outstanding organising activity was accomplished by a superb clinician, an excellent and generous teacher and one of a number of the great men responsible for the growth of and enthusiasm for Cardiology in Australia in the 1950's and 1960's. A clear thinker, an excellent communicator, author of many scientific papers, above all he was admired by both his patients and colleagues. Accompanying this was a great generosity of spirit, which gave support to many aspiring young doctors at that time. With his ready smile, his extraordinarily youthful appearance and his gusto for conversation both medical and non-medical, he was a delight to all who knew him.

In the late 1960's, Muriel and John left their lovely home in Sydney for planned retirement in Moss Vale. Here John spent his time reading, gardening and listening to his beloved chamber music. His presence in the district, however, quickly led to his being used as a cardiac consultant by his medical colleagues in the area. When he himself suffered a cardiac illness in the mid 1970's, he determined to retire from medical practice. John and Muriel had three children - Peter, a surgeon, Janet, an architect, and James, a lawyer and well-known wine expert. They were a very close and supportive family, always assisting greatly especially when it proved necessary for their parents to return to Sydney. Here John continued his great interest in his colleagues, his music, his reading and his bridge, as well as being a loving companion to Muriel, who at this time had become blind. He remained very active until his death in December 1990.

During his university days he and his brother George were excellent tennis players. After the war he did not continue tennis but played golf and bowls - not, however, with the same success. He was an accomplished bridge player and a member of Sir Herbert Schlink's well-known club. John's other outdoor activity, apart from gardening which he loved, was fly fishing in which he was a true expert, teaching his art to many grateful friends and colleagues. Being a left-hander he was able to explore the side of the river most found so difficult, and well into his 80's he undertook his annual trip to the Snowy Mountains and was as successful as ever. He sadly missed Muriel, who died in 1986, and withstood his own medical tribulations with patience and fortitude. Contributing enormously to cardiology, the Royal Australasian College of Physicians, the Cardiac Society, the National Heart Foundation and to insurance medicine, he was a remarkable and gracious man.