His male-line ancestors were wealthy agricultural and urban landowners in both countries, among the Anglo-Irish Protestant Ascendancy.

His brother, Richard Wellesley, Earl of Mornington, looked around and discovered that a manor in the parish of Wellington was available.

At the time he became Ambassador to France, The London Gazette of 4 June 1814 refers to him as having that title but suggests that it was granted by warrant on 25 August 1812.

Apart from the British titles, the Dukes of Wellington also hold the titles of Prince of Waterloo (Prins van Waterloo, 1815) of the Kingdom of the Netherlands, Duke of Ciudad Rodrigo (Duque de Ciudad Rodrigo, 1812) of the Kingdom of Spain with Grandeeship, and Duke of Victoria (Duque da Vitória, 1812), with the subsidiary titles Marquess of Torres Vedras (Marquês de Torres Vedras, 1812) and Count of Vimeiro (Conde de Vimeiro, 1811) of the Kingdom of Portugal.

He also has a large estate outside Granada, Spain, which was granted to the first duke by Spanish King Ferdinand VII as a reward for his services in the Peninsular War.

The dukedom of Ciudad Rodrigo in the Spanish peerage, together with its subsidiary titles, will continue to be held in the female line of descendants of the first Duke.

The earldom and barony of Mornington, along with the viscountcy of Wellesley, which are all titles in the Irish peerage, will revert to the line of the Earl Cowley, a male-line descendant of a younger brother of the first Duke of Wellington.