At the age of twenty Smillie received his first art lessons from his father, James Smillie, an eminent steel engraver. Shortly thereafter, he studied landscape painting briefly with James MacDougal Hart. In 1862 he opened a studio in New York City and exhibited for the first time at the National Academy of Design, where he was elected an associate in 1864. Smillie spent most of his professional life in New York, but sketched for several summers in the White Mountains and in the Adirondacks. In 1871, he sketched in the Rockies and Yosemite Valley, and in 1874 in Florida.
In 1881 he married Nellie Sheldon Jacobs, formerly a pupil of his older brother, James D. Smillie, whith whom the couple subsequently shared a studio in New York. In 1885 George Smillie and his wife made an extended tour of Europe. He was elected an academician of the National Academy of Design in 1882 and served as recording secretary from 1892 to 1902. He was also an early member, and later an officer, of the American Water Color Society.
A member of one of the most active and influential families in the art circles of New York City, George Smillie was acquainted at an early age with his father's many engraved translations from such American landscapists as Thomas Cole, Asher Durand, and Jasper Cropsey. Quite naturally then, he was able to embrace a wide range of landscape subjects, from quiet New England meadows to bold mountain passages and rocky coastlines. His most popular subject matter, however, was to be found in the interior and along the shores of Long Island.
Peter Bermingham American Art in the Barbizon Mood (Washington, D.C.: National Collection of Fine Arts and Smithsonian Institution Press, 1975)