Elley made his first step out of the ranks by becoming a Cornet in his regiment on 14 June 1794. On 30 January 1796 he was promoted to Lieutenant, and 11 January 1800 was made a Captain-Lieutenant. Elley acquired promotion to Captain by Purchase on 17 March 1801 to Major on 15 December 1804, and to Lieutenant-Colonel on 11 March 1806. One famous act of heroism occurred at the Battle of Talavera, as he led the charge riding a white horse across unknown terrain. A chasm suddenly appeared before him and he was forced to jump it at full gallop. As he wrote in a letter to his sister Mrs Ellis, dated 30 July 1809:
remembered Sir John as his mentor in this extract from his autobiography from 1818: Sent to Ireland following the war, he was promoted to Major-General in August 1819, and was presented with the Order of the Bath by King George IV at Dublin Castle in August 1822. He was appointed the Commander of Connaught, and then Governor of Galway from 1826 – this position was not filled after his death. On 23 November 1829 he was appointed Colonel of the 17th Lancers, replacing Lord Edward Somerset. At the state funeral of George IV on 15 July 1830 Elley was one of the group of senior Army and Naval officers who supported the canopy of purple velvet over the body of the King as it was taken to St George's Chapel, Windsor Castle, for the funeral service. He was elected Member of Parliament for Windsor in Robert Peel's Tory government. In 1836 the Eton & Windsor Gazette complained of the undue influence of the Castle on elections for that seat: Elley was promoted to Lieutenant-General on 10 January 1837.
Death and legacy
Sir John Elley died on 23 January 1839 at Cholderton Lodge at East Cholderton, part of Amport in Hampshire and was buried at St George's Chapel, Windsor Castle, not far from another of his properties at Burghfield Hill. His tomb includes a bust in black and whitemarble. His portrait, held by the National Portrait Gallery, was painted about 1837 as a study for the famous William Salter painting Waterloo Banquet At Apsley House, 1836, which depicts a commemorative banquet held by the Duke of Wellington at his London home on the anniversary of the battle. Though unmarried, Sir John was believed to have fathered at least one illegitimate son, who, legend has it, emigrated to Van Diemen's Land. In his will, dated 6 April 1838, Sir John left nothing to any member of his family. However, an Isabella Elizabeth Elley, daughter of the Reverend William Gifford Cookesley, of Eton College, was to receive a legacy of £300. The main beneficiary of the will was Sir John's housekeeper, Jane Carter. She was to receive a sizable portion of the contents of his home, a legacy of £2,000 and £300 a year for life. Jane's sister, Mary, was left a sum of £200 and £50 per year and her brother Edward £100 and £25 per year. The Officers Mess of the Horse Guards was to receive a legacy of £300 for the purchase of plate. Various charities also benefited from the will, as follows: