After graduating in 1916 with a degree in zoology, she taught math and science at a girls school in Vermont for one year.

The same year, she married Donald E. Lancefield, a fellow graduate student in genetics at Columbia.

Working with Avery and Dochez, she identified four serological types that classified 70 percent of the β-hemolytic streptococcal strains they were studying.

She named this protein the M-protein because a matt colony occurs when the bacteria is exposed to the antigen.

[8] Lancefield discovered that the group-specific antigen of streptococci was composed of carbohydrates, which she named the C-carbohydrate.

[8] This realization prompted her development of a classification system, called Lancefield grouping, for streptococcal diseases.

[8] During World War II, Lancefield served on the Commission on Streptococcal and Staphylococcal Diseases of the Armed Forces Epidemiological Board.

Lancefield was a long-time collaborator of Maclyn McCarty and a mentor of Emil Gotschlich, two recipients of the notable Lasker Prize.

[1] Lancefield's recipe for eggnog has been used by her fellow scientists for decades and was published on Science Friday.

[9] Due to Lancefield's willingness to answer microbiological questions, her lab at Rockefeller earned the nickname "the Scotland Yard of streptococcal mysteries.