Kondratiev was born in New York to a French mother and a Russian father. Raised in rural France near the site of ancient Celtic remains, he was inspired to learn the Irish language, first from books he found in libraries, then by living four years in the Aran Islands among native speakers.
For 25 years he taught Irish language at the Irish Arts Centre in New York as well as courses on Celtic mythology, early Celtic Christianity, and the history of Celtic traditional music. He was scholar guest of honor at the 2002 Mythcon in Boulder.
 Bibliography, selected