One of the first practicing landscape architects in Texas, Gunn was born in Florida and received a master’s degree from Harvard’s Graduate School of Design in 1930. Returning to Florida, Gunn was hired to design the original 55-acre Key West Botanical Garden. Shortly thereafter, he began working as chief engineer for E.A. McIlhenny of Jungle Gardens Nursery in Louisiana; for this nursery he participated in large-scale design projects of the Baton Rouge campus of Louisiana State University and the Louisiana state government complex. In 1943, Gunn opened a branch of the nursery in Houston, working as both plantsman and landscape architect on large projects such as the Shamrock Hotel. In 1952, Gunn was hired by Harris Masterson III to design the landscape for their home, Rienzi, now part of Houston’s Museum of Fine Arts. In 1956, Gunn began his largest single project: the restoration of the landscape for Rosedown Plantation in St. Francisville, LA. At the height of his career, Gunn designed more than two hundred residential landscapes in Houston’s exclusive River Oaks neighborhood. In addition, he worked on a number of historic Texas properties, including Liendo Plantation in Hempstead and Centennial House in Corpus Christi.