He was the youngest son of Scottish parents, Agnes Wilson and David Mushet; an ironmaster, formerly of the Clyde, Alfreton and Whitecliff Ironworks.

In the summer of 1848, Henry Burgess, editor of The Bankers' Circular, brought to Mushet a lump of white crystallised metal which he said was found in Rhenish Prussia.

The metal was run from the furnace into shallow iron troughs similar to the old refiners' boxes, and the cakes thus formed, when cold and broken up, showed large and beautifully bright facets and crystals specked with minute spots of uncombined carbon.

"[6] Mushet carried out many experiments with the metal, discovering that a small amount added during the manufacture of steel rendered it more workable when heated.

It was not until 1856, however, that he realised the true potential of this property when his friend Thomas Brown brought him a piece of steel, made using the Bessemer Process, asking if he could improve its poor quality.

This had the effect of improving the quality of the finished product, increasing its malleability – its ability to withstand rolling and forging at high temperatures.

In that year his 16-year-old daughter, Mary, travelled to London alone, to confront Bessemer at his offices, arguing that his success was based on the results of her father's work.

In 1861, Mushet invented the 'Dozzle'; a clay cone or sleeve, heated white hot and inserted into the top of the ingot mould near the end of the pour, and then filled with molten steel.