Beardmore's father died shortly afterwards and the retirement of the third business partner saw William's uncle Isaac become sole proprietor. William became a junior partner in 1879 and on his uncle's retirement seven years later he became the sole proprietor of the business. He rapidly expanded the business and formed it into the limited company of William Beardmore & Company, of which he became chairman and managing director, in 1902. In 1899, he bought the world-famous yard of Robert Napier and Sons at Govan, on the Clyde. In 1900 he became chairman of J. I. Thornycroft & Co, the torpedo boat builders. In 1902 he also became a shareholder and director of the armaments firm Vickers and the motor manufacturers Arrol-Johnston.