Wellesley was born in Dublin, into the Protestant Ascendancy in Ireland. He was commissioned as an ensign in the British Army in 1787, serving in Ireland as aide-de-camp to two successive Lords Lieutenant of Ireland. He was also elected as a Member of Parliament in the Irish House of Commons. He was a colonel by 1796, and saw action in the Netherlands and in India, where he fought in the Fourth Anglo-Mysore War at the Battle of Seringapatam. He was appointed governor of Seringapatam and Mysore in 1799 and, as a newly appointed major-general (since 1802), won a decisive victory over the Maratha Confederacy at the Battle of Assaye in 1803.
Wellesley rose to prominence as a general during the Peninsular campaign of the Napoleonic Wars, and was promoted to the rank of field marshal after leading the allied forces to victory against the French Empire at the Battle of Vitoria in 1813. Following Napoleon's exile in 1814, he served as the ambassador to France and was granted a dukedom. During the Hundred Days in 1815, he commanded the allied army which, together with a Prussian army under Blücher, defeated Napoleon at Waterloo. Wellington's battle record is exemplary; he ultimately participated in some 60 battles during the course of his military career.
Wellington is famous for his adaptive defensive style of warfare, resulting in several victories against numerically superior forces while minimising his own losses. He is regarded as one of the greatest defensive commanders of all time, and many of his tactics and battle plans are still studied in military academies around the world.
After the end of his active military career, Wellington returned to politics. He was twice British prime minister as part of the Tory party: from 1828 to 1830, and for a little less than a month in 1834. He oversaw the passage of the Catholic Relief Act 1829, but opposed the Reform Act 1832. He continued as one of the leading figures in the House of Lords until his retirement and remained Commander-in-Chief of the British Army until his death.
Wellesley was born into an aristocratic Anglo-Irish family in Ireland as The Hon. Arthur Wesley, the third of five surviving sons (fourth otherwise) to Anne and Garret Wesley, 1st Earl of Mornington. His mother was the eldest daughter of The 1st Viscount Dungannon. As such, he belonged to the Protestant Ascendancy. His biographers mostly follow the same contemporary newspaper evidence in saying that he was born on 1 May 1769, the day before he was baptised. His birthplace is uncertain. He was most likely born at his parents' townhouse, 24 Upper Merrion Street, Dublin, now the Merrion Hotel. But his mother Anne, Countess of Mornington, recalled in 1815 that he had been born at 6 Merrion Street, Dublin. Other places have been put forward as the location of his birth, including Mornington House (the house next door on Upper Merrion), as his father had asserted; the Dublin packet boat; and the mansion in the family estate of Athy (consumed in the fires of 1916), as the Duke apparently put on his 1851 census return.
He spent most of his childhood at his family's two homes, the first a large house in Dublin and the second Dangan Castle, 3 miles (5 km) north of Summerhill on the Trim Road (now the R158) in County Meath. In 1781, Arthur's father died and his eldest brother Richard inherited his father's earldom.
He went to the diocesan school in Trim when at Dangan, Mr Whyte's Academy when in Dublin, and Brown's School in Chelsea when in London. He then enrolled at Eton College, where he studied from 1781 to 1784. His loneliness there caused him to hate it, and makes it highly unlikely that he actually said "The Battle of Waterloo was won on the playing fields of Eton", a quotation which is often attributed to him. Moreover, Eton had no playing fields at the time. In 1785, a lack of success at Eton, combined with a shortage of family funds due to his father's death, forced the young Wellesley and his mother to move to Brussels. Until his early twenties, Arthur showed little sign of distinction and his mother grew increasingly concerned at his idleness, stating, "I don't know what I shall do with my awkward son Arthur."