The sitter wears the uniform of a Cornet of the 11th Light Dragoons. He did not reach the rank of Lieutenant-Colonel until 1798. He has a portfolio on his knees, and is drawing with a porte-crayon, drawing being, for the army officer, a vital accomplishment for recording fortifications and strategic positions. The author Robert Louis Stevenson wrote of this portrait in 1876, ‘The whole pose, the whole expression, is absolutely direct and simple. You are ready to take your oath to it that Colonel Lyon has no idea he was sitting for his picture, and thought of nothing in the world but his own occupation of the moment’. This was executed the year after Raeburn's return from Italy, when he was using paint of rich and creamy texture, unlike the flat square strokes of some of his later pictures.