Good was the son of a high-school principal who died of cancer when Good was five. Born in Crosby, Minnesota, he was educated at the University of Minnesota where he simultaneously obtained an MD and PhD in 1947. After this triumph he joined the Minnesota staff and served as professor of pediatrics from 1954 until 1973 when he moved to New York as director of the Sloan-Kettering Institute for Cancer Research. In 1982 Good moved to the University of Oklahoma as professor of microbiology, a post held until 1985, when he was appointed to a similar position in the University of South Florida, Tampa.

One of the great achievements of modern immunology has been the demonstration that the immunological system is not a simple unity but rather a complex interrelationship of a number of different units. The unraveling of this particular tangle was not the work of any one man or, indeed, any one group; Good's contribution was, however, as great as any other.

In the 1940s he showed a link between plasma cells, cells found in lymphoid tissue, and antibodies. Later he noted a simple tendency to recurrent infection among his patients suffering from myeloma (a tumor of bone-marrow cells) despite an abundance of plasma cells. This suggested to Good that there must be more to the immune system than simply the ability to make antibodies. This was reinforced when examining patients with agammaglobulinemia, who had no plasma cells at all, yet who were immunologically active enough to reject foreign skin grafts.

In the mid 1950s Good realized that there are two parts to the immune system: one dealing with defenses against typical bacterial infections; the other more concerned with clearing up ‘foreign’ or unusual cells. By 1961, independently of Jacques Miller, Good was beginning to suspect that the thymus gland was deeply implicated in providing the latter type of immunity.

Work on chickens' defense mechanisms against bacterial infection had demonstrated that if the bursa (a gland found in the chicken's alimentary canal) was removed, the creature lost the ability to make antibodies in any real quantity. They were in fact just like Good's agammaglobulinemic patients.

Good therefore postulated that there must be two types of immunity – one related to the thymus and the other related to the human equivalent of the chicken bursa producing antibodies. The details of the two systems and their evolution and interrelationship called for major, and as yet far from complete, research programs by immunologists.

Good became a leading proponent of the view that cancer is somehow the result of an immunological defect, a failure of the system to recognize and destroy the cancerous cell before it has begun to proliferate.