Brownrigg was a businessman as well as a doctor and scientist. He went into partnership with Anthony Bacon from Whitehaven in 1765 to develop the iron industry in Wales which led to the expansion of Merthyr Tydfil, particularly the Cyfarthfa Ironworks. He also inherited a share of John Speddings ropery and invested in the Keswick Turnpike Trust.
With his retirement to Ormathwaite, he became interested in improving the local agriculture, made a study of minerals, and encouraged Thomas West to write A Guide to the Lakes, the first guide book to the Lake District. He had several society positions including magistrate, Patent searcher at Port Carlisle and Receiver General of Government Taxes for Cumberland and Westmorland.
Brownrigg died in 1800 and was buried at Crosthwaite church where his coffin was carried by three baronets and other local gentry. His friend and biographer Joshua Dixon felt that his importance and abilities had been overlooked due to his modesty and reluctance to leave his home county of Cumberland in later life.