He was born into an Aromanian family in Avdella (Avdhela), a village that formed part of the Ottoman Empire's Manastir Vilayet and is now in Greece.
Papahagi taught high school in Ottoman Thessaloniki and Bitola, in Bulgarian Silistra, and in Giurgiu, Romania.
His first published work, which appeared in Analele Academiei Române in 1893, was a collection of children's folklore, Jocuri copilărești.
His contributions also appeared in Analele Dobrogei, Arhiva, Convorbiri Literare, Frățil’ia, Grai bun, Grai și suflet, Jahresbericht des Instituts für rumänische Sprache zu Leipzig, Peninsula Balcanică, Revue historique de sud-est européen, Viața nouă, and Viața Românească.
[2] An acknowledged authority on the life and languages of the Romance-speaking peoples from south of the Danube, the Aromanians and Megleno-Romanians, he wrote several foundational texts on the subject that are classic models of sociological and folkloristic monographs.