His portraits are remarkable for subtly capturing the individuality and personality of the sitters; his most ardent admirers think he is equaled in this only by Velázquez. Sargent's Portrait of Madame X (Madame Pierre Gautreau), done in 1884, is now considered one of his finest works, but it aroused so much negative reaction in Paris at the time that it prompted Sargent to move to London.
Although Sargent spent less than one year in the United States, some of his finest work is there, especially his decorations for the Boston Public Library. Sargent is usually not considered an impressionist, but he sometimes used impressionistic techniques to great effect, and his Claude Monet Painting at the Edge of a Wood is beautifully rendered in an impressionist style.
Around 1910 Sargent largely abandoned portraits, focusing mostly on landscapes in his later years.
In an era when the mainstream of art was focused on Impressionism and emphasizing artistic individuality, Sargent emphasized his own form of Realism and regularly worked doing commissioned portraits of the rich. This caused him to be dismissed as an anachronism at the time, but appreciation of him as a great artist has grown since his death.