Creighton was born in Halifax, Nova Scotia, the eldest son of William Hudson Creighton and Anna Fairbanks, grandson of James G. A. Creighton, founder of the James G. A. Creighton and Son ship chandling and wholesale food business. He was educated at Halifax Grammar School, where he graduated at age 14, then earned an arts degree with honours from University of King's College in 1868. He then studied under Sandford Fleming, who as engineer-in-chief for the Intercolonial Railway, hired him to work on surveys in Nova Scotia. Creighton moved to Montreal in 1872 and was employed as an engineer on the Lachine Canal, Montreal Harbour, and other public works. He was elected an associate of the Institution of Civil Engineers of Great Britain in 1876 and then attended McGill University, where he earned a bachelor's degree in common law, graduating with first class honours in 1880. On July 9, 1880, he was called to the Quebec bar, and two years later he became a partner in the firm of Barnard, Beauchamp, Creighton, and Doucet of Montreal.