A young girl reclines in a large blue armchair, her body relaxed and one arm draped over the back, while her gaze drifts to the side. She wears a white dress trimmed with lace, a dark plaid sash tied around her waist, and matching ribbons in her hair, with her legs stretched out and feet resting on the seat. To the left, a small dog with a dark coat lies curled up on another blue armchair, its head resting on the fabric and its body partially hidden by the folds.

The room is furnished with several overstuffed armchairs, all upholstered in vivid blue fabric patterned with loose, impressionistic strokes of pink, yellow, and green. The brushwork is energetic and visible, especially in the rendering of the blue fabric, where broad, quick strokes suggest both the texture of the upholstery and the play of light. The composition places the girl and the dog diagonally opposite each other, creating a sense of spaciousness and informal domesticity within the living room setting.

A third blue armchair appears in the background, partially obscured by the two chairs in the foreground and positioned near the back wall. The upper background features three tall window panes, their glass rendered with loose, pale brushstrokes that suggest daylight filtering into the room. Light falls most strongly on the girl's face, arms, and legs, creating gentle highlights on her skin and the white lace of her dress.

The lower right corner of the painting shows the curved arm and seat of another blue chair, cropped by the edge of the canvas. The floor is painted in a muted, brownish-grey tone, with soft, blended transitions that contrast with the energetic strokes of the upholstery. Fine, sketchy lines and dabs of color decorate the blue fabric, suggesting floral or abstract patterns in pink, yellow, green, and black throughout the armchairs. Little Girl in a Blue Armchair was painted by Mary Cassatt in 1878.

The painting belongs to the portrait genre and depicts a child, a dog, and a series of blue armchairs in a domestic interior.