In addition to his work as a publisher and essayist, Fields wrote poetry.
His chief works were the collection of sketches and essays entitled Underbrush (1877) and the chapters of reminiscence composing Yesterdays with Authors (1871), in which he recorded his personal friendship with William Wordsworth, William Makepeace Thackeray, Charles Dickens, Nathaniel Hawthorne, Herman Melville and others.