Smythe was Wyllie's older half-brother and the eldest of three illegitimate children that their mother, Katherine Benham, a singer, had with Percy Smythe, 6th Viscount Strangford (though the family always claimed a marriage). He was born in London on 4 September 1839 and spent his early years in France, where his younger sister and brother were born, though the family returned to London in 1843 and lived in Gloucester Crescent, Camden. Smythe was educated at King's College School and partly in France, which was where his mother met William Morrison Wyllie, an artist studying in Paris. They married and had two further sons, W.L.Wyllie himself being the first, born in London in 1851, and then Charles William, also a painter. All continued to spend holidays at Wimereux in Normandy, with Smythe and then W.L. Wyllie both attending the Heatherley School of Fine Art in London. Smythe - who encouraged his much younger Wyllie brothers - painted rural landscapes, genre and marine subjects, people and animals and was eventually associated with a group called the 'Idyllists'. He exhibited at the Royal Academy from 1863 (and became a full member in 1911) and the Royal Institute of Painters in Watercolours from 1881 (member, 1880), though he transferred his loyalty to the Royal Watercolour Society in 1892 (member, 1894). Smythe, his wife and three children settled at Wimereux in 1879, in a Napoleonic fortification, until this was destroyed by coastal erosion, after which they moved in 1882 to the more inland Château d'Honvault between Wimereux and Boulogne. The surrounding countryside and rural life remained his inspiration to his death.