Dennis studied at Colchester School of Art and this was followed by a three year diploma course at Norwich School of Art. He was elected an Associate of the Royal Watercolour Society in 1981 and a full member in 1983. His work has been commissioned by the National Trust, the Wardroom of the Royal Yacht Brittania, Sothebys, and American Express. He has exhibited at numerous Galleries throughout the UK and his work is now widely represented in public and private collections. He has been extensively published, most recently in two books of watercolours of Oxford and Cambridge Colleges.