Wittlin studied romance philology in Basel with Germà Colon, and later in Paris, Florence and Barcelona. He got his PhD in 1965 with a thesis about the Catalan translation of Brunetto Latini's Treasure by Guillem de Copons. He became Professor of Romance Philology and Historical Linguistics at the University of Saskatchewan in Saskatoon (Canada), where he arrived in 1967.
He has become a specialist in the edition of medieval translations in Europe of texts by Cicero, Saint Augustine and John of Wales, among others. He has also worked on Ramon Llull and on the history of medieval Catalan libraries. The Catalan writer to which he has devoted most of his life is Francesc Eiximenis. Wittlin has published most of the modern editions of Francesc Eiximenis' works and has written many studies and articles about Eiximenis.
In 1997 he became a member of the Institute of Catalan Studies and from 1990 to 1993 he was president of the North American Catalan Society. In 2000 he received the Creu de Sant Jordi (Saint George cross), a high distinction given by the regional Catalan government.
- Lo llibre de les dones d'Eiximenis (1980) with F. Naccarato
- Repertori d'expressions multinominals i de grups de sinònims en traduccions catalanes antigues (Nicolau d'Olwer price, 1989)
- La geometria secreta del tapís de Girona in Revista de Girona, 1991
- De la traducció literal a la creació literària (Serra d'Or prize 1996)
- Entorn de les edicions de textos medievals in Estudis Romànics, 2004
- (English) Biography in the University of Saskatchewan website.
- (French) Wittlin's works
- (Catalan) Article about Wittlin in the Great Catalan Encyclopedia