He attended the Regent Street Polytechnic and then the Royal School of Naval Architecture and Marine Engineering at South Kensington and at the same time, he began building the steam launch Nautilus in his father's study.

Nautilus was a fast boat with a reliable engine (also built by Thornycroft), and in 1862 it proved to be the first steam launch with enough speed to follow the contenders in the University race.

The ensuing publicity prompted his father to purchase a strip of land along the Thames, adjacent to Chesterman's yard at Chiswick in 1864, and that became the start of John Thornycroft's shipbuilding career.

On his return from Scotland Thornycroft built the fast steam yacht Miranda in 1871, and thereby proved that small vessels could obtain speeds that were not thought possible at the time.

[6][7] The exploits of Miranda gave rise to further orders of similar vessels, including Gitana, built in 1876 and capable of 20.8 knots (38.5 km/h; 23.9 mph), which was an astonishing speed at the time.

He bought the yacht Cecile of 300 tons and installed a device consisting of a 6-ton moveable watertank, controlled by hydraulic cylinders.

[15] In his quest for still faster vessels, John Thornycroft made several tests with different hull-shapes, eventually settling on a stepped hull for fast motor boats.

[17] The Hovercraft Museum holds a number of hull models that John Thornycroft used for his experiments, using air-flow as a mean of lifting boats out of the water.

[18] He was knighted in the 1902 Coronation Honours,[19] receiving the accolade from King Edward VII at Buckingham Palace on 24 October that year.