Reginald Punnett was born in England. As a young boy, Punnett suffered from appendicitis. During one of his recuperative periods, he started reading a series of books - Naturalist's Library. His father had bought the books because of the elegant binding; Punnett was fascinated by the subject. Although he went to Cambridge University as a medical student, Punnett graduated with a zoology degree in 1898. After graduation, Punnett continued at Cambridge as a researcher. He did work on the morphology of nemertine (ribbon) worms. Punnett has two species of marine worms named after him, Cerbratulus punnetti, Punnettia splendia.

While at Cambridge Punnett became interested in the experimental process, and wrote to William Bateson who was doing Mendelian experimentation on plants and animals. This began a scientific collaboration which helped establish "genetics" at Cambridge. Bateson and Punnett published the first account of gene linkage in sweet peas and Punnett developed the "Punnett Square" to depict the number and variety of genetic combinations.

Punnett had a role in connecting Mendelism with statistics. In 1908, Punnett was asked at a lecture to explain why recessive phenotypes still persist — if brown eyes were dominant, then why wasn't the whole country becoming brown-eyed? Punnett couldn't answer the question to his own satisfaction. He in turn asked his friend the mathematician, G. H. Hardy. Out of this conversation came the Hardy-Weinberg Law which calculates how population affects genetic inheritance.

In 1912, when William Bateson decided not to return to Cambridge, Punnett became the first Arthur Balfour Professor of Genetics at the university. He worked on the genetics of sweet pea, maize and poultry, developing many breeds. He even used linkage as a way to sex type baby chicks. Punnett continued to do experiments even after his retirement in 1940.

Punnett was a quiet, tolerant, cultured man who was excellent at all sport involving a small fast ball. At 80, he was still an active member of the Savile Club in London where he played snooker. He died at his home in Somerset, England at the age of 92.