Although "Thanatopsis", his most famous poem, has been said to date from 1811, it is more likely that Bryant began its composition in 1813, or even later. What is known about its publication in 1817 is that his father took some pages of verse from his son's desk, and at the invitation of Willard Phillips, an editor of the North American Review who had previously been tutored in the classics by Dr, Bryant, he submitted them along with his own work. The editor of the Review, Edward Tyrrel Channing, read the poem to his assistant, Richard Henry Dana, who immediately exclaimed, "That was never written on this side of the water!" Someone at the North American joined two of the son's discrete fragments, gave the result the Greek-derived title Thanatopsis ("meditation on death"), mistakenly attributed it to the father, and published it. After clarification of the authorship, the son's poems began appearing with some regularity in the "[Review]". "To a Waterfowl", published in 1821 was the most popular.
On January 11, 1821, Bryant, still striving to build a legal career, married Frances Fairchild. Soon after, having received an invitation to address the Harvard University Phi Beta Kappa Society at the school's August commencement, Bryant spent months working on "The Ages", a panorama in verse of the history of civilization, culminating in the establishment of the United States. As it would in all collections he subsequently issued, "The Ages" led the volume, also entitled Poems, which he arranged to publish on the same trip to Cambridge. For that book, he added sets of lines at the beginning and end of "Thanatopsis" that changed the poem. His career as a poet was now established, though recognition as America's leading poet waited until 1832, when an expanded Poems was published in the U.S. and, with the assistance of Washington Irving, in Britain.
His poetry has been described as being "of a thoughtful, meditative character, and makes but slight appeal to the mass of readers."