William G. Bennie, Xhosa linguist and educationist, was educated at the Lovedale mission station near Alice in the Eastern Cape where his father was a missionary of the Free Church of Scotland. His grandfather, John Bennie, a pioneer of the Glasgow Missionary Society, had also been a Xhosa linguist. William was placed first among 700 candidates in the School Certificate examination of the University of the Cape of Good Hope in 1885. After matriculating through the university in 1889 he obtained excellent results in his subsequent studies for the Bachelor of Arts degree, which was awarded to him by the same institution in 1893.
After teaching for a year at Lovedale Bennie was appointed in July 1894 as assistant deputy inspector of schools, and from 1897 as deputy inspector of schools in the Cape Colony. From April 1912 he was a "Grade A" inspector of schools in the Department of Education of the Union of South Africa. His work was characterised by painstaking care, scholastic competence, an interest in children and a love of the African people. In 1920 he was appointed to the new post of chief inspector of Native Education in the Cape Province. He was also a member of the governing council of the Lovedale Institution, a position from which he resigned in 1929. After his retirement from the Department of Education he taught Xhosa at the University of Cape Town until 1930. During the next decade he wrote A grammar of Xhosa for the Xhosa-speaking (Lovedale, 1939), edited two volumes of The Stewart Xhosa readers (1930) for junior and senior scholars, revised James McLaren's A concise Xhosa-English dictionary (1936), and published a paper on a national system of native education in the South African Journal of Science (1929). The University of Cape Town conferred an honorary Doctor of Laws (LLD) degree on him in 1940.
From about 1893 Bennie collected plants in the Albany Division and Kaffraria, Eastern Cape. His specimens went to the herbarium of the Albany Museum in Grahamstown. By 1911 he was a member of the South African Association for the Advancement of Science, serving as president of its Section E (which included education) in 1924.