A photographic pioneer, Llewelyn was using Talbot's calotype process within days of its announcement. He went on to marry Emma Thomasina Talbot (1806-1881), a cousin of Talbot. Llewelyn also developed his own oxymel photographic process in 1856. A founding member of the Photographic Society of London, later the Royal Photographic Society, he remained on the council until 1857.