There is much that is Romantic in the narrative account of Thomas de Quincey's own life that is comparable to other famous Romantic figures such as Keats and Shelley. You could start off by highlighting the way in which de Quincey suffered from ill health for much of his life and as a result was forced to take opium to alleviate the pain he was experiencing. Secondly, you might like to focus on his natural intelligence and the way that school and the traditional education system, based on principles of reason and rationality, had nothing to offer him, which set him off on a highly Romantic escape from his academic institution to the countryside of Wales. Lastly, you have the life of poverty that he led there and how he suffered great poverty both there and in London, where he went next.
Above all, however, it is the way that de Quincey uses opium, perhaps initially as a form of medication, but then in order to experience a higher or more exalted way of perceiving the world. This appeal to the imagination and the way that he records his opium-inspired reveries is very Romantic. Let us remember that one of the most famous Romantic poems in English literature, Coleridge's "Kubla Khan," was inspired whilst under the influence of opium.