American immunogeneticist who, with Jean Dausset (Dausset, Jean) and Baruj Benacerraf (Benacerraf, Baruj), was awarded the 1980 Nobel Prize for Physiology or Medicine for his studies of histocompatibility (a compatibility between the genetic (genetics) makeup of donor and host that allows a tissue graft from the former to be accepted by the latter).

Snell graduated from Dartmouth College in 1926 and received a Ph.D. in genetics from Harvard University in 1930. During 1931–33 he studied under the geneticist Hermann J. Muller (Muller, Hermann Joseph) at the University of Texas. In 1935 he joined the staff of the Jackson Laboratory in Bar Harbor, Maine, where he remained, becoming senior staff scientist in 1957, until his retirement in 1969.

At Bar Harbor, Snell, who was already immersed in mouse genetics, began to focus on the genetics of transplantation. His collaboration with British geneticist Peter Gorer led to the identification of a group of genes in the mouse called the H-2 gene complex, a term Snell coined to indicate whether a tissue graft would be accepted (the H stands for histocompatibility). Those histocompatibility genes encode cell surface proteins that allow the body to distinguish its own cells from those that are foreign—e.g., cells of a tissue graft or an infectious microorganism. The work resulted in the discovery of the major histocompatibility complex, a genetic complex found in all vertebrates that is analogous to the H-2 complex. Recognition of those genes paved the way for tissue and organ transplantation to become successful.

Snell was the author of a number of books, including Histocompatibility (1976), which he wrote with Jean Dausset and Stanley G. Natheson.