Born Edward Gordon Douglas, he was the younger son of the Hon. John Douglas and his wife Lady Frances (née Lascelles). James Douglas, 14th Earl of Morton, was his paternal grandfather and George Sholto Douglas, 17th Earl of Morton, his elder brother. He inherited the Penrhyn estate near Bangor in north-west Wales through his wife's relative, Richard Pennant, and changed his name to Douglas-Pennant by Royal license in 1841. Penrhyn was the owner of the Penrhyn Quarry near Bethesda, Wales, which under his ownership developed into one of the two largest slate quarries in the world. He was also involved in politics and sat as Member of Parliament for Caernarvonshire between 1841 and 1866. He also held the honorary post of Lord Lieutenant of Caernarvonshire. In 1866 he was raised to the peerage as Baron Penrhyn, of Llandegai in the County of Carnarvon.
Lord Penrhyn married, firstly, Juliana Isabella Mary, daughter of George Hay Dawkins Pennant, in 1833. They had two sons and three daughters. After her death in 1842 he married, secondly, Maria Louisa, daughter of Henry FitzRoy, 5th Duke of Grafton, in 1846. They had eight daughters. He died in 1886, aged 85, and was succeeded in the barony by his eldest son, George.