Stevens is a rare example of a poet whose main output came at a fairly advanced age. His first major publication (four poems from a sequence entitled "Phases" in the November 1914 edition of Poetry Magazine) was written at age 35, although as an undergraduate at Harvard, Stevens had written poetry and exchanged sonnets with George Santayana, with whom he was close through much of his life. Many of his canonical works were written well after he turned 50. According to the literary critic Harold Bloom, who called Stevens the "best and most representative" American poet of the time, no Western writer since Sophocles has had such a late flowering of artistic genius. Helen Vendler notes that there are three distinguishable moods present in Stevens' long poems: ecstasy, apathy, and reluctance between ecstasy and apathy. She also notes that his poetry was highly influenced by the paintings of Paul Klee and Paul Cézanne:
Stevens saw in the paintings of both Paul Klee—who was his favorite painter—and Cézanne the kind of work he wanted to do himself as a Modernist poet. Klee had imagined symbols. Klee is not a directly realistic painter and is full of whimsical and fanciful and imaginative and humorous projections of reality in his paintings. The paintings are often enigmatic or full of riddles, and Stevens liked that as well. What Stevens liked in Cézanne was the reduction, you might say, of the world to a few monumental objects.
Stevens's first book of poetry, a volume of rococo inventiveness titled Harmonium, was published in 1923. He produced two more major books of poetry during the 1920s and 1930s and three more in the 1940s. He received the annual National Book Award for Poetry twice, in 1951 for The Auroras of Autumn and in 1955 for Collected Poems.
Imagination and reality
Stevens, whose work was meditative and philosophical, is very much a poet of ideas. "The poem must resist the intelligence / Almost successfully," he wrote. Concerning the relation between consciousness and the world, in Stevens's work "imagination" is not equivalent to consciousness nor is "reality" equivalent to the world as it exists outside our minds. Reality is the product of the imagination as it shapes the world. Because it is constantly changing as we attempt to find imaginatively satisfying ways to perceive the world, reality is an activity, not a static object. We approach reality with a piecemeal understanding, putting together parts of the world in an attempt to make it seem coherent. To make sense of the world is to construct a worldview through an active exercise of the imagination. This is no dry, philosophical activity, but a passionate engagement in finding order and meaning. Thus Stevens would write in "The Idea of Order at Key West,"
- Oh! Blessed rage for order, pale Ramon,
- The maker's rage to order words of the sea,
- Words of the fragrant portals, dimly-starred,
- And of ourselves and of our origins,
- In ghostlier demarcations, keener sounds.
In his book Opus Posthumous, Stevens writes, "After one has abandoned a belief in God, poetry is that essence which takes its place as life’s redemption."  But as the poet attempts to find a fiction to replace the lost gods, he immediately encounters a problem: a direct knowledge of reality is not possible.
Stevens suggests that we live in the tension between the shapes we take as the world acts upon us and the ideas of order that our imagination imposes upon the world. The world influences us in our most normal activities: "The dress of a woman of Lhassa, / In its place, / Is an invisible element of that place / Made visible." Likewise, were we to place a jar on a hill in Tennessee, we would impose an order onto the landscape.
As Stevens says in his essay "Imagination as Value", "The truth seems to be that we live in concepts of the imagination before the reason has established them." The imagination is the mechanism by which we unconsciously conceptualize the normal patterns of life, while reason is the way we consciously conceptualize these patterns.
The imagination loses vitality as it ceases to adhere to what is real. When it adheres to the unreal and intensifies what is unreal, while its first effect may be extraordinary, that effect is the maximum effect that it will ever have.
Throughout his poetic career, Stevens was concerned with the question of what to think about the world now that our old notions of religion no longer suffice. His solution might be summarized by the notion of a "Supreme Fiction," an idea that would serve as a fictive replacement for the idea of God, known to be fictive but willfully believed. In this example from the satirical "A High-Toned Old Christian Woman," Stevens plays with the notions of immediately accessible, but ultimately unsatisfying, notions of reality:
- Poetry is the supreme Fiction, madame.
- Take the moral law and make a nave of it
- And from the nave build haunted heaven. Thus,
- The conscience is converted into palms
- Like windy citherns, hankering for hymns.
- We agree in principle. That’s clear. But take
- The opposing law and make a peristyle,
- And from the peristyle project a masque
- Beyond the planets. Thus, our bawdiness,
- Unpurged by epitaph, indulged at last,
- Is equally converted into palms,
- Squiggling like saxophones. And palm for palm,
- Madame, we are where we began.
The saxophones squiggle because, as J. Hillis Miller says of Stevens in his book, Poets of Reality, the theme of universal fluctuation is a constant theme throughout Stevens's poetry: "A great many of Stevens' poems show an object or group of objects in aimless oscillation or circling movement.” In the end, reality remains.
The supreme fiction is that conceptualization of reality that seems to resonate in its rightness, so much so that it seems to have captured, if only for a moment, something actual and real.
- I am the angel of reality,
- seen for a moment standing in the door.
- I am the necessary angel of earth,
- Since, in my sight, you see the earth again,
- Cleared of its stiff and stubborn, man-locked set,
- And, in my hearing, you hear its tragic drone
- Rise liquidly in liquid lingerings,
- Like watery words awash;
- an apparition appareled in
- Apparels of such lightest look that a turn
- Of my shoulder and quickly, too quickly, I am gone?
In one of his last poems, "Final Soliloquy of the Interior Paramour", Stevens describes the experience of an idea which satisfies the imagination, "This is, therefore, the intensest rendezvous. / It is in that thought that we collect ourselves, / Out of all the indifferences, into one thing.” This one thing is “a light, a power, the miraculous influence" wherein we can forget ourselves, sensing a comforting order, "A knowledge, that which arranged the rendezvous, / within its vital boundary, in the mind."
This knowledge necessarily exists within the mind, since it is an aspect of the imagination which can never attain a direct experience of reality.
- We say God and the imagination are one . . .
- How high that highest candle lights the dark.
- Out of this same light, out of the central mind
- We make a dwelling in the evening air,
- In which being there together is enough.
Stevens concludes that God is a human creation, but that feeling of rightness which for so long a time existed with the idea of God may be accessed again. This supreme fiction will be something equally central to our being, but contemporary to our lives, in a way that God can never again be. But with the right idea, we may again find the same sort of solace that we once found in divinity. "[Stevens] finds, too, a definite value in the complete contact with reality. Only, in fact, by this stark knowledge can he attain his own spiritual self that can resist the disintegrating forces of life . . . . Powerful force though the mind is . . . it cannot find the absolutes. Heaven lies about the seeing man in his sensuous apprehension of the world . . .; everything about him is part of the truth." 
- . . . Poetry
- Exceeding music must take the place
- Of empty heaven and its hymns,
- Ourselves in poetry must take their place
In this way, Stevens's poems adopt attitudes that are corollaries to those earlier spiritual longings that persist in the unconscious currents of the imagination. "The poem refreshes life so that we share, / For a moment, the first idea . . . It satisfies / Belief in an immaculate beginning / And sends us, winged by an unconscious will, / To an immaculate end." The "first idea" is that essential reality that stands before all others, that essential truth; but since all knowledge is contingent on its time and place, that supreme fiction will surely be transitory. This is the necessary angel of subjective reality—a reality that must always be qualified—and as such, always misses the mark to some degree—always contains elements of unreality.
Miller summarizes Stevens's position: "Though this dissolving of the self is in one way the end of everything, in another way it is the happy liberation. There are only two entities left now that the gods are dead: man and nature, subject and object. Nature is the physical world, visible, audible, tangible, present to all the senses, and man is consciousness, the nothing which receives nature and transforms it into something unreal . . . ."
From the first, critics and fellow poets praised Stevens. Hart Crane wrote to a friend in 1919, after reading some of the poems that would make up Harmonium, "There is a man whose work makes most of the rest of us quail." The Poetry Foundation states that "by the early 1950s Stevens was regarded as one of America's greatest contemporary poets, an artist whose precise abstractions exerted substantial influence on other writers." Some critics, like Randall Jarrell and Yvor Winters, praised Stevens' early work but were critical of his more abstract and philosophical later poems.
Harold Bloom, Helen Vendler, and Frank Kermode are among the critics who have cemented Stevens’s position in the canon as one of the key figures of 20th-century American Modernist poetry. Bloom has called Stevens "a vital part of the American mythology" and unlike Winters and Jarrell, Bloom has cited Stevens's laters poems, like "Poems of our Climate," as being among Stevens's best poems.
In 1976, at Atelier Crommelynck, David Hockney created a portfolio of twenty etchings called The Blue Guitar: Etchings By David Hockney Who Was Inspired By Wallace Stevens Who Was Inspired By Pablo Picasso. The etchings refer to themes of a poem by Stevens, "The Man With The Blue Guitar". The portfolio was published by Petersburg Press in October 1977. That year, Petersburg also published a book in which the poem's text was accompanied by the images.
Both titles of an early story by John Crowley, first published in 1978 as "Where Spirits Gat Them Home", later collected in 1993 as "Her Bounty to the Dead", come from "Sunday Morning".
John Irving quotes Stevens's poem "The Plot Against the Giant" in his novel The Hotel New Hampshire.
Nick Cave cited the lines "And the waves, the waves were soldiers moving" in his song "We Call Upon the Author". They come from Stevens's poem "Dry Loaf".
Vic Chesnutt recorded a song named "Wallace Stevens" on his album North Star Deserter. The song references Stevens's poem "Thirteen Ways of Looking at a Blackbird".
Julie Beman, a Hartford, Connecticut-based songwriter, wrote a song called "Hey There, Wallace Stevens." The song references Stevens's poems "Thirteen Ways of Looking at a Blackbird" and "The Man with the Blue Guitar."
Israeli songwriter Shlomo Artzi references "The man with the blue guitar" in his song "Romantic Story" ("The man with the blue guitar lifted his shirt to the stars").
Stephen King quoted Stevens's poem "The Emperor of Ice-Cream" in his novel 'Salem's Lot.
Australian musician Scott Kilminster named one of his albums "The Emperor of Ice-Cream".