In early life he was patronised by William Beckford the Younger of Fonthill, for whom he painted several sacred pictures, such as The Annunciation, The Temptation, The Agony in the Garden, and others.
He exhibited for the first time at the Royal Academy in 1844, sending a painting of a piece of still life which passed into Beckford's collection.
In 1847 he exhibited his first important picture, Naomi, Ruth, and Orpah; in 1849 he sent a portrait of Halil Aga Riskalla, and in 1850, one of the Turkish ambassadors, Mehemet Ali.
In 1852 he sent Aina Tellet, or the Light of the Mirror, and a portrait of the Duke of Hamilton.
Maddox painted several good portraits, of which there are many examples at Bath and at Bristol.