A teacher and author, Heini has spent his life teaching Welsh to children and adults, and from 1990 to 2003, he was a lecturer in the University's Department of Adult and Continuing Education. After taking early retirement from the department, he has continued to work as a translator and a language consultant.
Heini was raised in the city, a son of the writers and Egyptologists Kate Bosse Griffiths, the first Curator of the University's Egyptian Centre collection, and J Gwyn Griffiths, who taught Classics and Egyptology in Swansea University for over thirty years.
Heini is one of the main providers of material for Welsh learners. His extensive series of popular publications - including Welsh is Fun, the Welsh Learner’s Dictionary, and Street Welsh - are based on his solid academic research into the basic principles of language acquisition.