Letters of Elizabeth Cabot Cady Agassiz, undated

Elizabeth Cabot Cary was born in 1822 in Boston, Massachusetts, the daughter of Mary Ann Cushing Perkins Cary and Thomas Graves Cary. She had six siblings. Her health was delicate and she was educated at home, receiving history lessons from Elizabeth Peabody. In 1846, she met scientist and Harvard professor Louis Agassiz, who was then married to his first wife, Cecilie Braun Agassiz. Cecilie died in 1848 and Elizabeth and Louis married in 1850. Elizabeth thereby became stepmother to Louis's three children, with whom she developed close relationships. In 1856, Agassiz founded the Agassiz School for Girls in their home in Cambridge, Massachusetts; Louis Agassiz taught in the school and also arranged for other Harvard professors to teach classes. The school closed in 1863. In 1879, she became one of seven female managing directors of the Society for the Private Collegiate Instruction for Women (known informally as the Harvard Annex), which enabled women to have private classes from Harvard College professors. The Harvard Annex was incorporated in 1882, with Agassiz as president. She continued as president until 1903 and played a critical role in transforming the Annex into Radcliffe College in 1894.

In 1869, Agassiz became one of the first female members of the American Philosophical Society. She also helped to organize her husband's expeditions to Brazil (1865-1866) and the Strait of Magellan (1871-1872) and acted as the main writer and record keeper for these expeditions. She wrote the books A First Lesson in Natural History (1859, first published under the pseudonym Actaea); Seaside Studies in Natural History (1865, with her stepson Alexander Agassiz); and A Journey in Brazil (1868, with Louis Agassiz). She also edited Louis Agassiz: His Life and Correspondence (1885). Louis Agassiz died in 1873 and Agassiz died of a cerebral hemorrhage in 1907. They are both buried in Mount Auburn Cemetery in Cambridge, Massachusetts.