His style is defined by a soft, atmospheric quality that he learned from studying the works of Federico Barocci. Vanni used a palette of pale pinks and blues to create a sense of ethereal light. In works such as Saint Catherine of Siena Receiving the Stigmata and The Virgin and Child on Heavenly Throne, he focused on clear, emotional narratives. His figures possess a gentle grace that avoids the exaggerated poses found in earlier Mannerist art.

Modern collectors value Vanni for his ability to balance religious intensity with a calm, domestic scale. His drawings and etchings, such as his sketches of the crucifix, show a technical precision that translates well to paper prints. These works provide a window into the Counter-Reformation period without the heavy, dark tones often associated with that era. His compositions offer a serene atmosphere that suits contemporary living spaces.