Paul Dudley White, the distinguished cardiologist, wrote of Richard Cabot after his death:

In every generation there are restless souls who cannot be made to fit the common mold. A few of these are valuable in keeping their communities and professions in a ferment by their constant challenge to the existing order of man's thought and action. But when, in addition to possessing these attributes, a rare individual is endowed with the divine fire and makes important contributions to the pioneering progress of humanity, then indeed we recognize a great leader. In the thick of the fray such recognition comes slowly but as soon as the smoke of the battle clears the acclaim is universal. (1939)

Born into an old Bostonian family in 1868, Cabot was graduated from Harvard College in 1889 with a major in philosophy, his father's pursuit. After considering a career in the Unitarian ministry, he chose medicine and was graduated from Harvard Medical School in 1892 at age 24. His senior thesis was on "The Medical Bearing of Mind-Care," a study of healing by Christian Science.

During his internship at Massachusetts General Hospital, Cabot published a paper entitled "Leucocytosis as an Element in the Prognosis of Pneumonia" (see White, 1939), in which he described the elevated white blood cell count in pyogenic infections. Cabot spent the following year in hematologic research. His studies of blood culminated in his first book, A Guide to the Clinical Examination of the Blood, which was published in 1896 and went through five editions. In its preface he wrote, "the first book of its kind, so far as I am aware." Despite a busy private practice and service to outpatients at Massachusetts General Hospital, Cabot published a monograph, The Serum Diagnosis of Disease, in 1899, and another, Physical Diagnosis of Diseases of the Chest, in 1901. He expanded the latter book to include the rest of the body, writing twelve editions from 1901 to 1938. His book, Differential Diagnosis, published in 1938, went through seven editions. He emphasized errors of omission and commission in clinical diagnosis.

Cabot devoted much time to clinical research, gathering data from a large number of cases and then applying statistical analysis. He sought facts. After examining autopsy reports of 3000 cases, Cabot wrote in 1912 a controversial paper in which he pointed out "a goodly number of "classic" time-honored mistakes in diagnosis." In response to a Chicago physician who criticized his pessimism, Cabot wrote:

When he has had three thousand clinical diagnoses criticized at autopsy by an independent and unprejudiced pathologist who makes full bacteriologic and histologic examinations of every case, he will find, I believe, that the facts are not less unpleasant than I have stated them to be. He will know that his most scrupulous and careful examination of the precordia often fails to reveal acute pericarditis when it is present; that his examination of the urine will not always distinguish either acute or chronic nephritis from other conditions resembling them, and that mitral stenosis and aortic stenosis are sometimes overlooked by the best diagnosticians. (1913)

Cabot's paper on "The Four Common Types of Heart Disease" appeared in 1914 and is a landmark in medical history. For the first time, heart disease was classified according to its cause, which was a revolutionary point of view. He reported that 93% of 600 cases of heart disease were of either rheumatic, atherosclerotic, syphilitic, or nephritic etiology. Paul Dudley White (1939) described Cabot as the greatest contributor to cardiology in his generation.

After Walter B. Cannon introduced the idea of case teaching in medicine in 1900, Cabot became its most ardent advocate. His Exercises in Differential Diagnosis, published in 1902, consisted of 43 case summaries, each ending with the questions "Diagnosis? Prognosis? Treatment?" Cabot stressed the importance of deciding on a diagnosis and writing it down. He believed that "after the student has learned to open his eyes and see, he must learn to shut them and think" (1908). He considered the case method superior to other methods of teaching medicine. Wrote Cabot,

By using this method a single teacher can keep a large class of students actively busy. They are not merely listening or watching; they are doing the work of construction themselves. In lectures or large amphitheatre clinics the whole class is managed by one teacher, but the teacher does the work and hence the student's gain is relatively slight. (1908)

Cabot believed strongly in student participation, that the case method of teaching succeeds when the students are called on by name, that "only if no one in the class knows the answer should the teacher give it himself; for the process of answering serves to fix the fact in the student's mind and he should never be deprived of this benefit" (1908). The clinicopathologic conference, or CPC, was originated by Cabot in 1910, a result of his emphasis on the case study and the confirmation of a diagnosis by autopsy. His regular conference was held at Massachusetts General Hospital, a record of which was edited by him and published in the Boston Medical and Surgical Journal (now the New England Journal of Medicine) from 1924 to 1935.

Apart from his medical activities, Cabot gave much attention to social services, which he founded at Massachusetts General Hospital in 1905. His book, Social Service and the Art of Healing, appeared in 1909. Cabot's lifelong interest in ethics resulted in several books on the subject, and in 1919 at age 51, he was appointed professor of social ethics in addition to professor of clinical medicine. He was working on a philosophical treatise called "Creation" when he died in Boston in 1939.