A half-naked executioner stands at the center, gripping a sword and the wrist of a bearded man in black and white robes who collapses backward on the ground. Crowds of onlookers fill the left and right edges, their faces contorted in fear, horror, or astonishment; some recoil with raised hands, while others twist away or cover their faces. A woman in white at the right raises her arm in alarm, her body turned as if to flee, while a nearly naked man crouches at the lower left, his muscles tense as he tries to escape the violence.

The background is almost entirely dark, with only a few architectural hints and a shaft of light illuminating the central figures, creating a strong contrast between shadow and brilliance. Caravaggio uses dramatic chiaroscuro, with bold transitions between deep shadow and intense highlights, to focus attention on the martyr and his killer. The brushwork appears energetic and textured, especially in the flesh tones and drapery, giving a sense of immediacy and movement to the scene.

The figures are arranged in a tight, dynamic composition, their gestures leading the eye in a sweeping arc from the assassin’s outstretched arm to the angel above and back to the fallen saint. Details such as the feathered helmet of a soldier and the varied expressions of the crowd add layers of narrative and emotion to the scene. A winged angel descends from the upper right, emerging from a billow of clouds and extending a palm branch toward the fallen man.

In the upper left corner, a soldier in armor with a white plume on his helmet stands with his back turned, only his profile and helmet visible in the dim light. The lower right corner features a partially nude figure crouched and twisting away, his back and shoulders brightly illuminated. The background contains faint vertical architectural elements, including two columns barely visible behind the figures.

Light falls most strongly on the central executioner, the collapsing man, and the woman in white, leaving the rest of the scene in deep shadow. The painting’s colors are dominated by earthy browns, ochres, and pale flesh tones, with sharp, angular lines defining the limbs and drapery.