[2] Born in Kelso to a local farmer, Fairbairn showed an early mechanical aptitude and served as an apprentice millwright in Newcastle upon Tyne where he befriended the young George Stephenson.

In the 1840s, when Robert Stephenson, the son of his youthful friend George, was trying to develop a way of crossing the Menai Strait, he retained both Fairbairn and Hodgkinson as consultants.

It was Fairbairn who conceived the idea of a rectangular tube or box girder to bridge the large gap between Anglesey and North Wales.

The difficulties which were encountered in the construction of iron ships in an inland town like Manchester led to the removal of this branch of the business to Millwall, London in 1834–35.

Eventually this would lead to the near-universal adoption of water-tube boilers with small tubes for high pressures, replacing the older fire-tube designs.

Fairbairn was one of the first engineers to conduct systematic investigations of failures of structures, including the collapse of textile mills and boiler explosions.

His report on the collapse of a mill at Oldham showed the poor design methods used by architects when specifying cast iron girders for supporting heavily loaded floors, for example.

In another report, he condemned the use of trussed cast iron girders, and advised Robert Stephenson not to use the concept in a bridge then being built over the river Dee at Chester in 1846.

Fairbairn conducted some of the first serious studies of the effects of repeated loading of wrought and cast iron girders, showing that fracture could occur by crack growth from incipient defects, a problem now known as fatigue.