He was the third son of Francis Homfray (1674-1736), of Wales, a village in Rotherham located in the county then known as the West Riding of Yorkshire, and Mary Jeston (d.1758) of The Heath, Worcestershire. His father had been successful in the iron trade in Coalbrookdale, Staffordshire, and he made his home at Wollaston Hall, Worcestershire, and at Stourton Mill. He married Hannah Popkin of Coytrahen, near Bridgend, Glamorgan. In order to ensure a livelihood for his sons, Jeremiah, Thomas and Samuel Homfray, he approached Anthony Bacon (with whom he subsequently quarrelled) in September 1782 and leased an ironworks from him, to be used mainly for manufacturing weapons and ammunitions. The eventual result was the establishment of the Penydarren works at Merthyr Tydfil.
Welsh iron production went from 4000 tons per year in 1750 to 80000 in 1815.