Mackworth was born at Betton Grange, Shropshire some time in 1757, and died 25 August 1727, probably in London. His grandfather, also called Humphrey, was an officer in the New Model Army; his father was a gentleman of Shropshire. Mackworth matriculated at Magdalen College, Oxford in 1674 and entered the Middle Temple in 1675, and was called to bar 1682. He was knighted by James II in 1685, shortly after latter's accession to throne. In 1676 he married a wealthy heiress and acquired the Welsh estate of Gnoll and extensive coal-mining interests around Neath. He spent the next ten years developing this property and acquiring other interests in coal, silver and copper mines in the area. He established a company, the Mine Adventurers, with the Duke of Leeds as governor and himself as deputy-governor. Initially, large sums of capital were ploughed into the concern and the Neath coal mines became the largest in the country.
From The Biographical Dictionary of British Economists in Oxford Reference.