Louis Laybourne Smith (1 April 1880 – 13 September 1965) was an architect and educator in South Australia. Born in the Adelaide inner-southern suburb of Unley, he became interested in engineering and architecture while in the goldfields of Western Australia and later studied mechanical engineering at the School of Mines, serving an apprenticeship under architect Edward Davies. After graduating he accepted a position as a lecturer at the school, and was responsible for developing the first formal architecture course in the State in 1904. Between 1905 and 1914, he served as registrar at the school before leaving to join his long-time friend, Walter Bagot, at the architectural firm of Woods, Bagot and Jory. He remained with the firm until his death in 1965, and over the years was involved in a number of significant projects, including the South Australian National War Memorial and the original Australian Mutual Provident building on King William Street.
Along with his teaching and professional duties, Laybourne Smith was a member of the South Australian Institute of Architects, the Federal Council of the Australian Institute of Architects, and the Australian Institute of Architects, as well as being on numerous committees and advising the State Government in the formation of both the State Building Act of 1923 and the 1939 Architects Act. Today, the architectural school which he founded (now part of the University of South Australia) bears his name—the Louis Laybourne Smith School of Architecture.