It was in 1817 he founded a small ironwork at Willenhall, and seven years later joined his twin brother, Edward Thorneycroft, in establishing the Shrubbery Ironworks at Wolverhampton. The rise of the railways at that period, and the consequent larger demands for iron and steel, were among the causes which led to his great prosperity as an ironmaster.
His Willenhall residence was on the site now occupied by the Metropolitan Bank, in the Market Place: while his works, this first this iron magnate owned, were located near what is now known as Forge Yard, Waterglade Street. It was in this house his son, Colonel Thorneycroft, of Tettenhall Towers, was born.
His prominence as a public man may be estimated by the fact that when Wolverhampton was incorporated in 1848, Mr. Thorneycroft was selected for the honour of being first Mayor of the new borough. He was at all times a generous supporter of every local charity and benevolent institution, till the old quotation came to be fitted to him:—
There was a man—the neighbours thought him mad—
The more he gave away, the more he had.
In the Town Hall of Wolverhampton a statue has been set up to commemorate the public work of this estimable character.
Although during the greater portion of his career a great supporter of the State Church, in earlier life Mr. G. B. Thorneycroft had been an ardent Wesleyan; and in his memoirs (p. 134) it is recorded how he liquidated the burden of debt on the Willenhall Chapel belonging to that denomination. On his death, in 1851, among those who testified to his public usefulness, and the estimation in which he was held, was the Rev. G. H. Fisher, of Willenhall (memoirs pp. 263–5).
“The Willenhall Magazine” was the name of a monthly periodical launched in 1862, “published for the proprietors by J. Loxton, Market Place, Willenhall,” and having Messrs. J. C. and Jesse Tildesley as its chief contributors. The first number appeared in March, and twelve months afterwards this praiseworthy attempt to establish a local magazine in Willenhall had completely failed.