She received her BA in 1964 from Harvard and her PhD in 1970 from Indiana University Bloomington, with a dissertation entitled Problems in Finnish Phonology.
[6] In her linguistics career Karttunen has specialised in the study of Mesoamerican languages such as Mayan but in particular Nahuatl, on which topic she has authored seven books and numerous academic papers.
Early in her career Karttunen also produced several studies of Finnish phonology and syntax, including her 1970 dissertation.
As a historian Karttunen has published research in areas such as historical Mesoamerican literature, colonial-era Aztec and Nahua history, and the social organizations, socio-political concerns and literacy rates of indigenous peoples of Mexico.
She followed this by an article on Nahua literacy, showing how the Mesoamerican tradition of pictorial writing then transitioned to alphabetic writing in Latin letters by local-level notaries in a self-perpetuating tradition.