He began his career as an artist by winning the silver medal offered by the Duke of Sussex for a drawing of Hercules, and afterwards was a student at Finden's house, where he was intimate with Hablot Knight Browne, who was similarly employed.
He drew pictures of the tournament at Eglinton Castle for the ‘Illustrated London News.’ His fondness for natural history displayed itself chiefly in observations on the habits of fish and waterside birds.
He also wrote 'The Rail and the Rod,’[2] a meritorious guide book to the favourite angling resorts of the Thames.
Generous to a fault, and an excellent practical angler, Fennell was never so happy as when relating to a circle of friends reminiscences of Dickens, Thackeray, Douglas Jerrold, Mackay, and Harrison Ainsworth, with all of whom he had been on intimate terms.
He lived long at Barnes, and late in life at Henley, at both of which places he was favourably situated for the pursuit of angling.