A man stands full-length, turned slightly to his right, against a backdrop of stone architecture and a cloudy sky tinged with the warm light of sunset. He wears a black doublet and matching breeches, the dark fabric catching the light in subtle folds and reflecting a soft sheen. A voluminous black cloak drapes over his shoulders, edged with a broad, elaborate white lace collar that frames his face and extends down over his chest.

His right hand holds a black hat at his side, while his left arm rests on his hip, the hand partly concealed by the folds of his cloak and the hilt of a gold sword. A blue sash crosses his chest from the left shoulder, adding a vivid diagonal accent to the otherwise restrained palette. The man's face is framed by shoulder-length, curled brown hair and a carefully groomed mustache and goatee; his gaze meets the viewer directly, with a composed, self-assured expression.

Delicate lace cuffs emerge from the sleeves, their intricate patterns rendered with precise, light brushwork that contrasts with the broader, more fluid handling of the cloak and background. The stone balustrade at the right edge of the composition anchors the figure in space, while the sky behind him glows with streaks of orange and grey, suggesting the close of day. The lower part of the painting is dominated by deep shadows, with the figure's boots and the ground beneath him barely emerging from darkness.

Fine, smooth brushwork is visible in the rendering of the face and hands, while broader, more atmospheric strokes shape the cloak and background. Portrait of William Cavendish, Duke of Newcastle (1592-1676) was painted by Anthony van Dyck in 1640. The subject, William Cavendish, 1st Duke of Newcastle, is depicted in formal attire, emphasizing his status and dignity.