His paintings were exhibited beginning in 1878. He won the Mention of Honor in 1881 and a Third Class medal in 1888. Thornley embraced the Impressionist movement early in his career, which brought him much success.
His style characteristically has bold brushwork and thick "impasto." It recreates the "impression of a panorama", capturing the fleeting moment in its inner light and color. This open landscape is an example of what the artist excelled at: successful color effects which are highly decorative but stay true to nature.