Joseph Coen was born at Yass in southern New South Wales where his father was a successful businessman. Educated at St Ignatius College, Riverview and at St John's College, University of Sydney, he graduated in medicine in 1905. He was a good student and a first-class sportsman, gaining university blues in football and rowing. After residency training at St Vincent's Hospital, Sydney he spent about a year in postgraduate work in England and Ireland before returning to set up as a general practitioner in the northern New South Wales town of Lismore. He married Clara Chilcott shortly before starting practice. She bore him five children (one of whom became a surgeon) and throughout his life she remained a strong, even formidable, force behind him.

He spent about twenty years as a country general practitioner, a demanding and all-embracing occupation with little available specialist help. In 1927 he decided to specialise in internal medicine. After visiting the United States to study recent developments, he returned to Sydney with an electrocardiograph - a rather rare instrument in Australia at that time - and set up as a consultant in Macquarie Street with a back-up general practice in Vaucluse. He was appointed honorary physician to Lewisham Hospital and the NSW Community Hospital and his practice grew rapidly. A few years later he was able to cease his general practice and continue exclusively as a consultant. When the College was founded in 1938 he was made a foundation Fellow.

He was a kind man, liked by colleagues and patients equally. Success came to him because of his humanity and his clinical skills acquired in nearly fifty years of practice. In spite of cardiac failure which troubled him for some years, he continued in practice until eighteen months before his death at the age of seventy-eight.