William was a butcher, however he soon switched careers and began a seven-year apprenticeship with George Clarke, the famous Marine Engineers of Sunderland.

After completing his apprenticeship, Mills spent seven years at sea, obtaining a first class Certificate as a Marine Engineer in 1884.

During his time at sea Mills witnessed great loss of life caused by the unsafe engaging and disengaging methods used on ship lifeboats.

After leaving the sea, Mills went into business as a General Engineer in Sunderland in 1885, when he established the first Aluminium foundry in the United Kingdom at The Atlas Works, Bonnersfield.

Besides the hand grenade and golf clubs, Mills was also the inventor of the Patent Instantaneous Engaging and Disengaging Gear for Ships and Boats.

Mills was an active member of the Executive of the Birmingham Chamber of Commerce, Chairman of the James Watt Centenary Committee and, in his spare time, a collector of pictures, china and antiques.