He is known for his work on the first treatise to explore the practice of musical notation of rhythm, De Mensurabili Musica.
Sources writing about Garlandia in the late 13th and early 14th century also call him a magister, indicating he probably had a role as a teacher at the University of Paris.
In this system, notes on the page are assigned to groups of long and short values based on their context.
De mensurabili musica describes six rhythmic modes, corresponding to poetic feet: long–short (trochee), short–long (iamb), long–short–short (dactyl), short–short–long (anapest), long–long (spondee), and short–short (pyrrhic).
Modal rhythm is the defining rhythmic characteristic of the music of the Notre Dame school, giving it an utterly distinct sound, one which was to prevail throughout the 13th century.