An elderly man sits in the lower right foreground, his legs extended and crossed, dressed in a golden yellow cloak over a red robe, writing in a large book resting on his knee. Near his right side, a dark-feathered eagle stands on the ground, its head turned toward him, identifying the figure as Saint John of Patmos. Fragments of ancient architecture—broken columns, a square pedestal, and scattered stone blocks—lie around Saint John, suggesting the ruins of a classical world.

Behind him, a winding path curves up a rocky slope, bordered by dense greenery and two tall trees that rise at the right edge of the painting. Across the middle ground, lush green trees and bushes are arranged in orderly masses, framing a view toward a broad river or bay that stretches into the distance. On the left, a large tree with a thick trunk and rounded canopy stands in front of the water, while further back, a cityscape is faintly visible along the shore.

The background features a sunlit landscape with rolling hills and a mountain, bathed in soft, natural light under a blue sky dotted with billowing white clouds. Dominating the center, the ruins of a grand classical temple with tall columns and a partially collapsed pediment rise above the trees, accompanied by an upright obelisk. The light falls evenly across the scene, illuminating Saint John, the ruins, and the distant landscape, while casting gentle shadows beneath the trees and architectural fragments.

Poussin arranges the composition with measured order, aligning the architectural forms and landscape elements parallel to the picture plane, creating a sense of serenity and balance. The brushwork appears smooth and controlled, with crisp outlines and subtle gradations of color that reinforce the clarity and harmony of the scene. The color palette is dominated by earthy browns, deep greens, and the warm ochre of Saint John's cloak, contrasted with the cool blues and whites of the sky and distant water. Saint John is depicted here as an elderly man, though Christian tradition often regards him as the youngest of Christ’s disciples.

The eagle beside him is his traditional attribute, reinforcing his identity. The idealized landscape is filled with references to Greco-Roman civilization, including the column fragments, obelisk, and temple, suggesting the passage from the ancient world to Christianity.