He spent most of his professional life in New York City, but he and his brother, James David Smillie, traveled West to the Rocky Mountains and Yosemite Valley in 1870. Two years later, he went to Europe, which resulted in a more forceful style and lightened palette. He also traveled in the Adirondacks and the White Mountains of New Hampshire. Late in his career, he adopted the Impressionist style.
In 1881, he married Nellie Sheldon Jacobs, a pupil of his brother's, and the three of them shared a studio. He was introverted, and after the death of James in 1909, he lived as a solitary artist in the Bronxville.