In 1895 Hobby began working for the Houston Post as a circulation clerk. Later he became a business writer for the newspaper. This was followed by the posts of city editor and managing editor. In 1907 he left the newspaper to become manager and part owner of the Beaumont Enterprise.
Hobby was an active member of the Democratic Party and eventually became secretary of the state executive committee. Hobby was elected lieutenant governor in 1914 and governor of Texas in 1917. At 39, Hobby was the youngest man to hold the office. Hobby became an important figure during the First World War as over half of the country's military camps and most of its airfields were located in Texas. Hobby is credited with setting up an effective military draft system in Texas during the final two years of the war.
After completing his term of office, Hobby returned to the Beaumont Enterprise. Later he was to acquire the Beaumont Journal. In 1924 he became president of the Houston Post. With the help of Jesse H. Jones, Hobby became the owner of the newspaper in 1939. The Houston Post Company also owned the radio station, KPRC, and the television station, KPRC-TV.
Hobby became a member of what became known as the Suite 8F Group. The name comes from the room in the Lamar Hotel in Houston where they held their meetings. Members of the group included Lyndon B. Johnson, George Brown and Herman Brown (Brown & Root), Jesse H. Jones (multimillionaire investor in a large number of organizations and chairman of the Reconstruction Finance Corporation), Gus Wortham (American General Insurance Company), James Slither Abercrombie (Cameron Iron Works), Richard Russell (chairman of the Committee of Manufactures, Committee on Armed Forces and Committee of Appropriations) and John Connally (Governor of Texas). Alvin Wirtz and Edward Clark, were also members of the Suite 8F Group.
William Hobby died in Houston on 7th June, 1964. Three years after his death, the Houston International Airport, was renamed the Hobby Airport.