He received the doctorate in 1878 at the University of Göttingen with a dissertation on "The Emergence of the Indo-Iranian Palatal Series" (German: Die Entstehung der indoiranischen Palatalreihe), and his 1885 habilitation degree at the University of Halle for "The Inflection of Nouns with Threefold Gradation in Old Indic and in Greek: the Cases of the Singular" (German: Die Flexion der Nomina mit dreifacher Stammabstufung im Altindischen und im Griechischen – Die Casus des Singular).
In 1886, Collitz emigrated to the United States, where he taught at Bryn Mawr College in Philadelphia. In 1907, he moved to Johns Hopkins University in Baltimore, Maryland, where he took up a chair in Germanic studies.
In 1924, Collitz was elected the first president of the Linguistic Society of America. In 1927, he officially retired from Johns Hopkins, but remained in Baltimore until his death in 1935.
- Sammlung der griechischen Dialektinschriften (1884-1909; with Friedrich Bechtel).
- Die Verwandtschaftsverhältnisse der griechischen Dialekte (1895).
- Die neueste Sprachforschung (1886).
- World Languages in PMLA, Vol. 40, Appendix (1925), pp. xliii-lv, published by Modern Language Association
- "Hermann Collitz" in German Life magazine, December 2014/January 2015, p.57
- Hermann Collitz Catalogus Professorum Halensis (biography in German)