George Wyndham entered the Royal Navy in 1799 as a midshipman in HMS "Amelia". In 1802 he transferred to the Army as a Cornet in the 5th Dragoon Guards, promoted in 1803 to Lieutenant in the 3rd Dragoon Guards. In 1805 he was a Captain in the 72nd Highlanders and ADC to Sir Eyre Coote who was Lieutenant Governor of Jamaica. In 1807 he was DAAG to Earl Cathcart at the Bombardment of Copenhagen; in 1809, as Captain in the 1st Foot Guards, he took part in the Walcheren Expedition; in 1811 he was a Major in the 78th Regiment and the 12th Light Dragoons; and in 1812 he was Lieutenant-Colonel commanding the 20th Light Dragoons at the siege of Ciudad Rodrigo.