He invented a type of windmill sail and the prison treadwheel, and was employed as chief engineer, at Ransomes of Ipswich, before moving to London.

His father moved to Southrepps, and William at an early age was employed in the mill, but in 1800 was apprenticed to James Lyon, a cabinet-maker at Stalham, from whom he parted after four years.

At Bacton Wood Mills he again worked with his father in 1804, and also constructed a machine for splitting hides.

Self-regulating windmill sails were invented and patented by him in 1807, at which period he settled at Horning, Norfolk, in business as a millwright.

[3] Already Cubitt was concerned with the employment of criminals; and for the purpose of using their labour he invented the treadmill,[3] with the object, for example, of grinding corn, and not at first contemplating the use of the machine as a means of punishment.

[3] From 1814 Cubitt had been acting as a civil engineer, and after his move to London he was fully engaged in important works.

As engineer-in-chief he constructed the South Eastern Railway: he adopted the scheme of employing a monster charge of 18,000 lb.

The works for supplying Berlin with water were carried out under his direction; and he was surveyor for the Paris and Lyon railway.

Among his last works were the two large landing-stages at Liverpool, and the bridge for carrying the London turnpike road across the River Medway at Rochester, Kent.