As a teenager, he would work in his father's mill in Cedar Rapids, Iowa sweeping floors.
In 1899, Stuart's father and his business partner Henry Parsons Crowell had used a proxy fight to gain control of the American Cereal Company from Ferdinand Schumacher.
In 1907, at age 30, Stuart was named a director of the Quaker Oats Company and soon became thoroughly acquainted with the business.
In addition to his work at the Quaker Oats Company, Stuart sat on the board of directors of International Harvester, the Canadian Imperial Bank of Commerce, the Pennsylvania Railroad, and Northern Trust.
Also, in 1947, at the request of President of the United States Harry Truman, Stuart was a member of the Hoover Commission.