From 1958 to 1979, Yiannopoulos served on the faculty of Louisiana State University's Paul M. Hebert Law Center.
He also authored three volumes of the Louisiana Civil Law Treatise series, now in the fourth edition.
He directed the Tulane University Law School's summer programs in Greece since 1980.
At the time of his death, he was revising portions of the civil code, collecting materials for an admiralty textbook, and working on the next edition of his property treatise.
His revision of the Civil Code provisions on quasi-contracts became law in 1996, on representation and mandate in 1998, on deposit and sequestration in 2003, and on loan in 2004.