Crawshay and his younger brother Edmund took over the management of Hawks, Stanley & Co., an established ironworks at Gateshead and the rapid expansion that followed can be largely attributed to the Crawshays' expertise in securing government contracts. By the mid-1840s the ironworks of Hawks, Crawshay & Sons had become the largest on Tyneside, employing more than one thousand workers. It produced a vast range of iron goods, including anchors, chains, and boiler plates, but its growing reputation primarily accrued from lucrative contracts to supply quality ironwork for bridges and lighthouses.
Among the most notable of these was the commission for Newcastle upon Tyne's High Level Bridge in 1849, an ambitious structure requiring some 5050 tons of ironwork. The firm also worked on the Iron Bridge at Sunderland. Foreign contracts quickly followed, and impressive bridges were constructed in Constantinople and Burma, and for the India State Railway. By mid-century, Crawshay's enterprises had earned him the popular nickname King of Gateshead.
Crawshay had political interests too and supported the Turks during the Eastern crisis of the mid-1870s. Midhat Pasha became a personal friend and was a frequent visitor at the family home, Haughton Castle. Crawshay was so highly regarded that he later acted as Turkish consul in Newcastle and, interestingly enough, is thought to have been the first person to introduce Turkish baths into England, installing a bath at his Tynemouth house.
By the 1870s and 1880s the Gateshead site declined compared with the more streamlined and specialised engineering yards established along the Tyne by entrepreneurs such as Sir William Armstrong. A crisis was reached in 1889, when the 'New Greenwich' ironworks of Hawks, Crawshay & Sons at Gateshead was suddenly closed. Crawshay was accused of incompetence and neglect in investing too heavily in new plant and failing to specialize, but the circumstances of the collapse remain somewhat mysterious. .