Born in Middlesex, England, Giles began his career as an apprentice to the architectural firm Giles and Bivens (senior partner John Giles was no relation) while studying art at the University of London. After completing his training, he worked briefly for Giles and Bivens before immigrating to the United States in 1873. He settled in San Antonio, Texas, joining the offices of John H. Kampmann, an architect and building contractor. In his three years with Kampmann, Giles became skilled in using Texas’ natural resources as building materials, particularly stone. He opened his own firm in 1876, where he served the prominent San Antonio community in designing domestic residences, including the Edward Steves Homestead, a three-story French Renaissance Revival-style mansion located in what is now the King William Historic District. He also designed the Carl Wilhelm August Groos House, an Italian-style villa completed in 1880.
By 1900 Giles had designed more than 40 commercial structures in San Antonio and at least eleven county courthouses across Texas, including the extant Caldwell and Goliad courthouses. At the turn of the century, he expanded his business to Mexico, opening a branch office in the city of Monterrey and designing buildings in Saltillo, Durango, Puebla, Chihuahua, and other locations. Notable buildings include the Banco Mercantil and Arco de la Independencia, both in Monterrey. Giles was known for designs characterized by limited ornamentation and a strong sense of symmetry. He served as chairman of the Texas State Association of Architects and was a member of the Society of San Antonio Architects. He died at his home on Hillingdon Ranch near Comfort, Texas, and is buried in San Antonio’s City Cemetery No. 1.