son of William David Jeffrey and Margaret (Lewis), was b. in 1797 at Llanddeusant, Carms. After serving as apprentice to his maternal uncle, Lewis Lewis, a grocer and draper at Merthyr Tydfil, he opened a shop of his own at Hirwaun, and soon afterwards m. Mary Lewis, who seems to have been a daughter of Thomas Lewis, another uncle of his. They did well, built larger premises, reared five sons and five daughters, and were the mainstays of the young Welsh Wesleyan cause at Hirwaun. As the family grew up, Davis was able to leave the shop to the care of his wife and children, and to tap another source of income by opening a small coal level on Cefn Rhigos; this colliery (with its wharf at Briton Ferry) was sold in 1847, but long before that, Davis had taken a lease of valuable steam-coal seams on the Blaen-gwawr estate at Aberaman, and began sinking a pit there in 1843, using first (1845) the canal and, afterwards (1847), the new Taff Vale Railway to get his coal down to Cardiff. Leaving the Hirwaun shop in charge of his second son, Lewis (below), he now placed his eldest son, David (below), in a shop at Trecynon (Aberdare); and as a number of his workmen had now migrated from Hirwaun to work at Blaen-gwawr, he promoted the erection, in 1850, of the present Welsh Wesleyan chapel at Aberdare. So far, he himself had continued to live at Hirwaun; but about 1851 he began sinking a new pit at Aber-cwmboi, lower down the Aberdare valley. He thereupon ceased to live at Hirwaun, and built himself a house at Blaen-gwawr, also giving up the Trecynon shop, and building a house (‘Maes-y-ffynnon’) for his son, David, who now joined him in the supervision of the collieries; soon, too, the Hirwaun shop was sold, and Lewis Davis was placed at Cardiff as sales agent for the coal.
David Davis, sen., now turned his attention to the Rhondda Fach valley, hitherto not only unexploited, but almost trackless. After costly but at first unsuccessful sinkings, he finally struck a good seam at the place which is now called Ferndale — the colliery plant and machinery had to be horse-hauled over the intervening ridge from Aberdare. In 1865, Davis and other coalowners, in protest against the heavy charges levied at the Bute (Cardiff) Docks, opened a new dock at Penarth. At the beginning of 1866 he brought his sons, David, Lewis, Frederick, and William, into the partnership ‘Davis and Sons.’ He d. 19 May 1866, aged 69, and was buried in S. John's churchyard at Aberdare; his widow d. 11 Sept. 1877.
After Davis's death the firm opened more pits at Ferndale. In 1867 William Davis retired and, in 1876, Frederick Davis d. The two surviving brothers carried the business on.