Academic and clinical career
- Graduated from Trinity College, Dublin in 1908
- Received a masters degree in dental science in 1909
- Undertook specialist orthodontic studies under Edward Angle in the United States
- Established the first orthodontic practice in Dublin, the first in the British Isles
- Appointed as Lecturer in Orthodontics at Trinity in 1910
- Received a Doctor of Science degree in 1928
- Became the first professor of orthodontics in Europe in 1941
- Pioneered the use of stainless steel for orthodontic devices
- Conducted research on muscle testing and training, jaw size and form, tooth migration, and occlusion

Professional societies
- Founder member of the British Society for the Study of Orthodontics
- Served as president of the society in 1924
- President of the Irish Dental Association in 1932
- President of the European Orthodontic Society from 1935 to 1937
- President of the Odontological Section of the Royal Society of Medicine in 1949
- Advocated for the specialization of orthodontics in Britain
- Campaigned for greater professionalization of orthodontics
- Encouraged non-specialist dentists to refer orthodontic cases to specialists

Awards and fellowships
- Awarded Fellowship of the Royal College of Surgeons of England in 1948
- Awarded Fellowship of the Royal College of Surgeons of Edinburgh in 1951
- Received the Villain Prize in orthodontics from the Fédération Dentaire Internationale in 1957
- Became the first person outside North America to receive the Ketcham Award from the American Board of Orthodontics in 1960
- Elected an honorary fellow of Trinity College Dublin in 1962

Legacy
- Three years after Friel's death, his family provided funding for the annual Sheldon Friel Memorial Lecture by the European Orthodontic Society
- Friel's contributions to orthodontics and his pioneering use of stainless steel continue to influence the field
- His establishment of the first orthodontic practice in Dublin paved the way for the development of orthodontics in the British Isles

References
- Lee, John B. (1972). The history of the Irish Dental Association, 1922–1972.
- Wahl, Norman (2005). Orthodontics in 3 millennia. Chapter 4: The professionalization of orthodontics (concluded).
- Obituary. The Journal of the Irish Dental Association. 16: 43. 1970.
- Taylor, Geoffrey Stuart; Malcolm Nicolson (July 2007). The Emergence of Orthodontics as a Specialty in Britain: The Role of the British Society for the Study of Orthodontics.
- Lee, John B.; Niall J. Hogan (1992). The evolution of a profession and of its dental school in Dublin. Atrium Productions.