Guillem has taught and given demonstrations on the technique of icon painting in numerous museums and monasteries in Europe and the United States, and has undertaken many church commissions. He is a founding member of the Association of Iconographers of Ireland, and a Patron of the Association of British Iconographers. He was Head of Fine Art at Kensington and Chelsea College, London (1990-2004). He now paints full time and also teaches advanced painting at Morley College. His book The Technique of Icon Painting, was first published in the UK by Search Press in 1990.