He attended the Hotchkiss School and then completed a course of studies at the Yale University, graduating in 1949.
[2] In 1953, he earned a medical doctoral degree at the Columbia College of Physicians and Surgeons.
[3] Cahill started working as a medical assistant at the Biochemical Department at the Peter Bent Bringham Hospital (today: Brigham and Women’s Hospital) in Boston.
He was also involved in research at the Albert Baird Hastings laboratory from 1955 until 1957 before he transferred to the Joslin's Diabetes Center in 1958, after another clinical year.
There, he took the place of research director when Albert Renold returned to Europe 1962.