Gruelle is best known for his landscape paintings, as well as his book, "Notes: Critical and Biographical: Collection of W. T. Walters" (1895). Gruelle's art from the time he spent at Gloucester, Massachusetts, are among his best, especially his watercolors. Among his most notable paintings were a series of marine scenes that included "The Drama of the Elements". Gruelle’s masterwork, "The Canal––Morning Effect" (1894), is a painting of the Indianapolis skyline from the south side of the city's Military Park. The Art Association of Indianapolis quickly acquired the painting, and it remains in the collection of the Indianapolis Museum of Art. Gruelle only occasionally exhibited his works in national exhibitions, with two notable exceptions. He exhibited at the Society of Western Artists annual shows and in 1904 at the Louisiana Purchase Exposition at Saint Louis, Missouri. Gruelle preferred one-man shows held in Indianapolis, Indiana, and in New Canaan, Connecticut.