William Kennedy, petroleum geologist, was born in Scotland. He spent some time at the University of Edinburgh, but it is not known if he ever received a degree. His early training was for the merchant marine, but his parents objected to this calling because it kept him away from home. He went into the banking business and was transferred to the Bank of British North America in Halifax, Nova Scotia. While in banking Kennedy became interested in geology. He was versed in surveying instruments and mathematics. By systematic reading and study he rapidly became a proficient geologist and published his first paper on geology in 1884. In the late 1880s he abandoned banking and accepted a position with J. C. Branner on the Arkansas Geological Survey. In 1890 Kennedy joined the Dumble survey (officially the Geological and Mineralogical Survey of Texas, later called the Texas Geological Survey).
Kennedy's first Texas assignment was to investigate the iron ores of East Texas, and two reports of his findings were published in 1891. During his work with the Dumble he was the primary geologist working on the Texas Coastal Plain. He mapped many of the counties in this part of Texas and described many of its Tertiary sections. With the refusal of the legislature to continue funding the Texas Geological and Mineral Survey in 1895, its director, Edwin T. Dumble, was hired by the Southern Pacific Railroad; he took with him many of the former employees of the survey, including Kennedy, who became an employee of the Rio Bravo Oil Company, the subsidiary of Southern Pacific that supplied fuel to the railroad and administered its lands. Kennedy's knowledge of the Texas coast made him ideal for exploring and supervising the petroleum potentials of that area. When the Spindletop oilfield discoveries brought on a renewed interest in petroleum, Kennedy began to explore for the hydrocarbons trapped in salt domes. Shortly after 1901 he coauthored a report with C. W. Hayes for the United States Geological Survey on the oilfields of the Texas and Louisiana Gulf Coastal Plain; the report, a seminal work in petroleum geology, was published in 1903. After working with Rio Bravo Oil and the United States Geological Survey, he spent the remainder of his career consulting in petroleum and mining.
Kennedy married Margaret S. Richardson in Hamilton, Ontario; they had two sons, neither of whom outlived his parents. Kennedy died on February 23, 1926, in Fort Worth.