Stewart Ferguson was born at Wodonga, Victoria, the son of a barrister and civil servant, and was educated at South Melbourne College. He graduated from the University of Melbourne when barely twenty-two and gained his doctorate when only twenty-four. He spent over two years on the resident staff of the Melbourne Children's Hospital - a long period for these days - and in 1907 became a clinical assistant to outpatients. He joined the honorary medical staff in 1912 as physician to outpatients and in 1914, still only thirty-two, he became a physician to inpatients. That position he held until he died twenty-five years later, when he was the Hospital's senior physician. For years he was also honorary medical officer to the Infant Asylum, East Melbourne.

Stewart's early specialisation grew into a life-long dedication and he became, to quote a contemporary (Hume Turnbull), `a great children's doctor’. His major contribution was the care of children at all ages, especially in infant feeding and in the wise management of difficult children and parents. Kind, wise and helpful to all, he was very popular, with a large specialist practice, and yet he found time to follow up patients at home all over Melbourne. In the ward he would carefully study the infant's history, signs and especially the stools before prescribing the feeding. Almost invariably, the baby responded.

Soon after the College was formed, Stewart's health declined and he died of a coronary occlusion. He had been a popular teacher with considerable influence on infant welfare in Victoria. However, despite his early scholastic success, he did not feature in scientific advances and he 'spoke little in public and wrote less' (Turnbull). He could be dogmatic too, and he and Jock Grieve (the other leading paediatrician) taught conflicting feeding methods, which confused the students, so two junior paediatricians had to write a manual for them. Nevertheless his standing in the profession generally was very good, and he served on the BMA council for five years, one of them as honorary secretary.

Stewart was a man of few words, sometimes even a bit austere. However he was fond of society, had a friendly and kindly manner, was a golfer and a good raconteur, and had many friends outside his profession. He was fond of the arts, with a special appreciation of repertory plays. He enjoyed a very happy family life until his first wife died of tuberculosis. They had one son, who was killed on active service with the RAAF, and one daughter. Stewart's second marriage was to Lillian Tudehope.