Kriaras was born in Piraeus in Attica, Greece, on 28 November 1906 to a family of Cretan origin[1] and spent his early childhood on the island of Milos, the southwesternmost of the Cyclades.

Some of his research was on Erotókritos the early 17th century romantic epic which represents the high point of renaissance literature in Crete.

This work was published in 1938 as Essays concerning the sources of Erotókritos (Μελετήματα περί τας πηγάς του Ερωτοκρίτου) for which he was awarded his doctorate by the University of Athens.

Probably his most important work has been the Lexicon of Medieval Greek Demotic Literature 1100-1669 (Λεξικό της μεσαιωνικής ελληνικής δημώδους γραμματείας 1100-1669), published since 1968 and now supplemented with a 2-volume condensed edition.

His Greek Dictionary of the Modern Demotic Language, Written and Oral (Νέο ελληνικό λεξικό της σύγχρονης ελληνικής δημοτικής γλώσσας, γραπτής και προφορικής) (1995) is the most authoritative modern Greek monolingual dictionary.