[3] She completed her PhD in linguistics at Yale University in 1935 at the age of 25, with a dissertation titled A Grammar of the Tunica Language.

[4] In the 1930s, Haas worked with the last native speaker of Tunica, Sesostrie Youchigant, producing extensive texts and vocabularies.

[6][7] Shortly after, Haas conducted fieldwork with Watt Sam and Nancy Raven, the last two native speakers of the Natchez language in Oklahoma.

[9] Her Creek texts were published after her death in a volume that was edited and translated by Jack B. Martin, Margaret McKane Mauldin, and Juanita McGirt.

[10][11] During World War II, the United States government viewed the study and teaching of Southeast Asian languages as important to the war effort,[12] and under the auspices of the Army Specialized Training Program at the University of California at Berkeley, Haas developed a program to teach the Thai language.

As a founder and director of the Survey of California Indian Languages,[18] she advised nearly fifty dissertations, including those of many linguists who would go on to be influential in the field, including William Bright (Karok), William Shipley (Maidu), Robert Oswalt (Kashaya), Karl Teeter (Wiyot), Catherine Callaghan (Penutian), Margaret Langdon (Diegueño), Sally McLendon (Eastern Pomo), Victor Golla (Hupa), Marc Okrand (Mutsun), Kenneth Whistler (Proto-Wintun), Douglas Parks (Pawnee and Arikara), and William Jacobsen (Washo).